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Remote Sensing of Turbidity in Seawater Intrusion Reaches of Pearl River Estuary – a Case Study in Modaomen Water Way, China
Abstract
Based on field experiments and analysis, the study examined the spectral characteristic and spatial variability of turbidity in the Pearl River Estuary by using the EO-1 ALI satellite imagery collected on December 18, 2005. A negative regression model (turbidity = −439.52 × R (570) + 22.913, R2 = 0.9042, n = 11) between the in-situ turbidity and the reflectance at 570 nm (maximum correlation spectral band between 350 and 2500 nm), resulting from increasing of organic matters in suspended solids, was built and applied to ALI band 4 (0.525–0.605 nm). Simple in-water spectral pairs calibration method of bright and dark targets provided the good atmospheric correction of ALI with a root mean square error of 0.00061, and mean absolute percentage error of 2.04%. The study also found the seawater turbidity is a more accurate indicator of Chl_a concentration (R2 = 0.7442) than TSS (R2 = 0.7061). Also, there is a large correlation between TSS and the turbidity (R2 = 0.86, N = 22) for Modaomen watercourse. The model-deduced turbidity distribution from ALI band 4 exhibited distinctive spatial variability of turbidity in the dry season, accordant with seasonal in-situ investigation. The ALI data provides accurate estimates of the mean water clarity conditions in the PRE (RMSE = 1.878 and MAPE = 11.7%) and has potential importance for water quality monitoring of optical remote sensing in the similar estuaries and its future operation.
... Besides TSS, other commonly used water quality indices include water clarity, turbidity, etc. The turbidity is a type of effect that is related to the concentration of TSS and other impurity elements in water and is observable from remotely sensed imagery [1]. It was found that variations in turbidity help understand the distribution of TSS and procedures like coastal erosions and mobilization of chemicals or pollutants [33]. ...
... Udy et al. (2005) [34] found a strong correlation between turbidity and TSS with a determination coefficient (R 2 ) of 0.88 in the central Great Barrier Reef Lagoon, Australia. [1] had a similar finding in his case study conducted in China, which also proved the correlation between the two. ...
... MODIS data have gained more attention in the application of TSS estimation in water bodies than Landsat TM data because of the improved spectral resolution (36 bands) with bands sensitive to water, higher temporal resolution (twice a day instead of 16 days interval of Landsat TM data) to capture highly dynamic water status before and after a storm, and a higher radiometric resolution sensitive to small changes of values. Previous studies of different water bodies such as small bay areas, lakes, and estuarine areas have reported strong correlations between water quality parameters and band 1 (620-670 nm in red) and band 2 (841-876 nm in near infrared or NIR) of MODIS imagery [1,43,44]. Therefore, this study selected band 1 and 2 for TSS estimation. ...
... Monitoring drinking water quality, turbidity and water quality in coastal and estuarine waters [40][41]; improving efficiency of hydroelectric reservoirs and assessing cumulative environmental alterations resulting from new dams [42,43]. Detecting thermal plume discharges from nuclear power stations [44]. ...
... Focusing on the Pearl River Estuary in southern China, Chen et al. [41] used RS data as a tool for ecosystem restoration by focusing on turbidity, defined as an "optical effect that is related to the concentration of total suspended solids (TSS) and the shape and size of other impure elements in water" [41]. The researchers recommend using EO-1 ALI satellite imagery (Earth Observing, Advanced Land Imager-10 and 30 m) [94] for water quality measurements in coastal and estuarine waters. ...
... Focusing on the Pearl River Estuary in southern China, Chen et al. [41] used RS data as a tool for ecosystem restoration by focusing on turbidity, defined as an "optical effect that is related to the concentration of total suspended solids (TSS) and the shape and size of other impure elements in water" [41]. The researchers recommend using EO-1 ALI satellite imagery (Earth Observing, Advanced Land Imager-10 and 30 m) [94] for water quality measurements in coastal and estuarine waters. ...
Remotely sensed (RS) imagery is increasingly being adopted in investigations and applications outside of traditional land-use land-cover change (LUCC) studies. This is due to the increased awareness by governments, NGOs and Industry that earth observation data provide important and useful spatial and temporal information that can be used to make better decisions, design policies and address problems that range in scale from local to global. Additionally, citizens are increasingly adopting spatial analysis into their work as they utilize a suite of readily available geospatial tools. This paper examines some of the ways remotely sensed images and derived maps are being extended beyond LUCC to areas such as fire modeling, coastal and marine applications, infrastructure and urbanization, archeology, and to ecological, or infrastructure footprint analysis. Given the interdisciplinary approach of such work, this paper organizes selected studies into broad categories identified above. Findings demonstrate that RS data and technologies are being widely used in many fields, ranging from fishing to war fighting. As technology improves, costs go down, quality increases and data become increasingly available, greater numbers of organizations and local citizens will be using RS in important everyday applications.
... Turbidity is an important parameter for water quality and a surrogate for the transparency of water [1][2][3][4][5].Turbidity can damage many aquatic organisms and fishes by degrading spawning grounds, reducing feed supplies, and affecting gill function [6]. A decrease or increase in water transparency can adversely affect the organic components of systems that adjust to light-dispersing environments [7][8][9][10][11][12][13][14][15]. ...
... In estuarine waters with high turbidity, dissolved oxygen concentrations can significantly decrease due to irregularities in heterotrophic and autotrophic processes, which may contribute to the depletion of marine organisms [16,17]. Typically, turbidity is assessed visually using a Secchi disk, or presumably through nephelometry [1,5]. However, these methods only represent the locations from which the sample was collected. ...
Nowadays, space-borne imaging spectro-radiometers are exploited for many environmental applications, including water quality monitoring. Turbidity is a standout amongst the essential parameters of water quality that affect productivity. The current study aims to utilize Landsat 8 surface reflectance (L8SR) to retrieve turbidity in the Ramganga River, a tributary of the Ganges River. Samples of river water were collected from 16 different locations on 13 March and 27 November 2014. L8SR images from6 March and 17 November 2014 were downloaded from the United States Geological Survey (USGS) website. The algorithm to retrieve turbidity is based on the correlation between L8SRreflectance (single and ratio bands) and insitu data. The b2/b4 and b2/b3 bands ratio are proven to be the best predictors of turbidity, with R2 = 0.560 (p < 0.05) and R2 = 0.726 (p < 0.05) for March and November, respectively. Selected models are validated by comparing the concentrations of predicted and measured turbidity. The results showed that L8SR is a promising tool for monitoring surface water from space, even in relatively narrow river channels, such as the Ramganga River.
... It is well known that to obtain reasonable water turbidity from satellite observations, an accurate retrieval algorithm is a key. Up to now, various retrieval algorithms have been developed in the past decades (Doxaran, Castaing, and Lavender 2006;Chen, Hu, and Muller-Karger 2007;Chen et al. 2009;Nechad, Ruddick, and Neukermans 2009;Dogliotti et al. 2015;Shi and Wang 2010;Gohin 2011;Choi et al. 2012Choi et al. , 2014Qiu et al. 2015). ...
... Satellite ocean colour data have an obvious advantage for studying the spatiotemporal variability in water turbidity due to its high spatiotemporal coverage. However, remote sensing of the water turbidity in the Eastern China Seas is still a challenging task, although many algorithms have been designed in various waters of the world oceans (Doxaran, Castaing, and Lavender 2006;Chen, Hu, and Muller-Karger 2007; Chen et al. 2009;Nechad, Ruddick, and Neukermans 2009;Shi and Wang 2010;Gohin 2011;Choi et al. 2012Choi et al. , 2014Dogliotti et al. 2015;Qiu et al. 2015). On the one hand, the often-failed atmospheric correction for aerosol in the highly turbid waters of the Eastern China Seas hinders the applications of the existing algorithms. ...
Water turbidity plays an important role in marine biogeochemical processes and ecosystem. Remote sensing of water turbidity in the Eastern China Seas is still a challenging task due to its large variations spanning more than three orders from coastal highly turbid waters to offshore clear waters. Thus, this study developed a new blended remote sensing algorithm for accurately estimating water turbidity in the whole Eastern China Seas from Geostationary Ocean Colour Imager (GOCI). The general idea of the new blended algorithm is to combine the band forms with the best abilities for deriving water turbidity in turbid waters and relatively clear waters, respectively. Evaluations based on field data showed a good performance of the new blended algorithm with values of the determination coefficient (R²), root-mean-square error (RMSE), mean absolute error (MAE), and mean relative error (MRE) of 0.884, 47.96 NTU, 29.59 and 48.13%, respectively. The proposed algorithm was applied to the GOCI data of 2015; and large spatiotemporal variations of water turbidity in the Eastern China Seas were observed. High values of water turbidity were observed in winter for both coastal and offshore waters, whereas the lowest values were observed in summer. Sediment resuspension drove by wind and tidal forcing, and sediment transportation related to current might be responsible for spatiotemporal variations of water turbidity, while the detailed study is required for further investigations. Overall, this study provides a technological basis which can be used to understand the variation patterns of water turbidity in the Eastern China Seas from GOCI satellite measurements.
... Many experiments and in-situ studies showed that reflectance increases with increasing TSS concentration in visible and near-infrared bands [26,27]. However, a negative correlation between reflectance and TSS was found in the Pearl River Estuary under condition of suspended solid adsorbing organic matter [28]. TSS concentration has a strong correlation to Chl-a concentration [29,28]. ...
... However, a negative correlation between reflectance and TSS was found in the Pearl River Estuary under condition of suspended solid adsorbing organic matter [28]. TSS concentration has a strong correlation to Chl-a concentration [29,28]. Dongshan Lake has lower reflectance than other three urban lakes at the blue and green bands of SPOT 5 (Luhu, Liuhua, and Liwan in Fig. 6). ...
... located at six cities of Guangdong Province and pours into South China Sea. As we all know estuary and coast of Pearl River suffers from severely combined pollution (Ma and Wang 2003) which mainly comes from industrial production, residential life and seawater intrusion (Chen et al., 2009a). ...
... With spectral coverage 25 ranging from 400 to 2500 nm and 10 nm (sampling interval) of contiguous bands of the solar reflected spectrum, Hyperion's spatial resolution is 30 m with a 7.7 km imagery swath and 185 km length (http://eo1.usgs.gov). Hyperion is also well suited for retrieving spatial distributions of water-color constituents in Pearl River Estuary (Chen et al., 2009a). The Hyperion data was just used for further and supplementary validation of TSS retrieving model here. ...
Retrieving total suspended solids (TSS) concentration accurately is essential for sustainable management of estuaries and coasts, which plays a key role in the interaction of hydrosphere, pedosphere and atmosphere. Although many TSS retrieval models have been published, the general inversion method that is applicable to different field conditions is still under research. In order to obtain a TSS remote sensing model that is suitable for estimating the TSS concentrations with wide range in estuaries and coasts by Landsat imageries, this study recalibrated and validated a number of regression-techniques-based TSS retrieval models using 129 in-situ samples collected from five regions of China during the period of 2006–2013. It was found that the optimized Quadratic model using the Ratio of Logarithmic transformation of red band and near infrared band and logarithmic transformation of TSS concentration (QRLTSS) works well and shows a relatively satisfactory performance. The adjusted QRLTSS model based on Landsat sensors explain about 72 % of the TSS concentration variation (TSS: 4.3–577.2 mg/L, N = 84) in the study and have an acceptable validation accuracy (TSS: 4.5–474 mg/L, RMSE: 21.5–25 mg/L, MRE: 27.2–32.5 %, N = 35). The QRLTSS model based on Landsat OLI is better than TM and ETM+ (R2: 0.7181 vs. 0.7079, 0.708) because of the optimization of OLI sensor's design. A threshold of red band reflectance (OLI: 0.032, ETM+ and TM: 0.031) was proved capable to help solve the QRLTSS model and retrieve TSS concentration from Landsat remote sensing imageries. After 6S model-based atmospheric correction of Landsat imageries, the TSS concentrations of three regions (Moyangjiang River Estuary, Pearl River Estuary and Hanjiang River Estuary) in Guangdong Province of China by OLI and ETM+ imageries were retrieved by the optimized QRLTSS model. As a result, the Landsat imagery inversed TSS concentrations showed good validation accuracies with the synchronous in-situ observation (TSS: 7–160 mg/L, RMSE: 11.06 mg/L, MRE: 24.1 %, N = 22). The TSS concentrations retrieved from Landsat imageries in the three estuaries showed large variation (0.295–370.4 mg/L). The further validation from EO-1 Hyperion imagery showed good performance of the model (In site synchronous measurement of TSS: 106–220.7 mg/L, RMSE: 26.66 mg/L, MRE: 12.6 %, N = 13) for the area of high TSS concentrations in Lingding Bay of Pearl River Estuaries as well. Evidently, the QRLTSS model can be potentially applied to simulate high-dynamic TSS concentrations of other estuaries and coasts in the world by Landsat imageries, improving the understanding of the spatial and temporal variation of TSS concentrations on regional and global scales. We believe that the optimized QRLTSS model can hopefully be further adjusted to establish a regional or unified TSS retrieval model of estuaries and coasts for different satellite sensors similar to Landsat OLI-ETM+-TM sensors or with similar red and near infrared bands, such as ALI, HJ-1 A/B, LISS, CBERS, ASTER, ALOS, RapidEye, Kanopus-V, GF, etc.
... Salinity information is very important to water resources management in PRE. Yet, at present, knowledge of salinity in PRE is limited because it is currently measured at thirteen hydrological stations by the Pearl River Water Resources Commission (PRWRC), Ministry of Water Resources, China, and it cannot provide spatial information of seawater intrusion and cannot meet the needs of water resources management [7]. Few studies use remotely sensed TSS (total suspended sediment concentrations) to estimate salinity in PRE [6][7], but there is little progress in estimating salinity using remotely sensed temperature. ...
... Yet, at present, knowledge of salinity in PRE is limited because it is currently measured at thirteen hydrological stations by the Pearl River Water Resources Commission (PRWRC), Ministry of Water Resources, China, and it cannot provide spatial information of seawater intrusion and cannot meet the needs of water resources management [7]. Few studies use remotely sensed TSS (total suspended sediment concentrations) to estimate salinity in PRE [6][7], but there is little progress in estimating salinity using remotely sensed temperature. SMOS SSS retrieval algorithm identified salinity and sea surface temperature (SST) has good relationship, but water in PRE is highly loaded of suspended solids, can salinity be retrieved using SST? Figure 1 Location of the study area Therefore, objective of this study is to investigate the relationship between salinity and sea surface temperature retrieved from remotely sensed image in PRE. ...
Sea surface salinity (SSS) is of great important to physical, biological, and chemical oceanographers. Although a challenge, it is possible to measure SSS from space using remote sensing data. However, existed SSS product is only useful for large scale research, i.e. open ocean (with area larger than of 200 × 200 km2), but may play a minor role at local scale study such as in monitoring seawater intrusion in estuary. Therefore, objective of this study is to investigate the relationship between salinity and remotely sensed sea surface temperature. A case study was carried out using MODIS sea surface temperature (SST) product and observational chlorosity in the Pearl River Estuary, China. The results concluded were that a polynomial regression model shows that salinity might be estimated using SST as the mean absolute error is 2.950/00 and in most cases absolute errors were less than 1.20/00.
... The Modaomen channel located in the PRE of China is the main stream of Xijiang and Beijiang River. As the primary channel of the eight outlets in the PRE (Song et al. 2014), it transports a significant amount of fresh water and sand (Chen et al. 2009) from the aforementioned two rivers into the coastal sea. In addition, it supplies water to nearby cities like Zhuhai and Macao. ...
In recent decades, the frequency and severity of inland river seawater intrusion has increased in the Pearl River Estuary (PRE) of China. Based on time series of water salinity data, river discharges, tides, and wind records for the period 2003–2015, this study aims to examine the regular pattern and underlying mechanisms of the seawater intrusion in the Modaomen channel of the PRE. Toward this end, the autocorrelation and spectral analysis are used to quantify the periodicity of runoff, tide, and water salinity and to infer the regular patterns of seawater intrusion. The Pearson correlation and the LMG metric are used to examine the effects of influencing factors on seawater intrusion. Results indicate that seawater intrusion in the Modaomen channel has distinct annual (369 days) and half-monthly (14.8 days) cycles, corresponding well with annual and half-monthly tidal cycles. Spatially, the frequency, severity, and periodicity of seawater intrusion decrease with increased landward distance away from the channel mouth. The prevention of seawater intrusion by incoming river flow becomes more remarkable as freshwater flows downstream. Shifts in wind speed and direction can strengthen or weaken seawater intrusion, depending on if wind is in the opposite or same direction of river flow. Further analysis using the LMG metric suggests that river discharge plays a dominant role in governing seawater intrusion. Overall, river discharges, tides, and wind are three major forces triggering the inland river seawater intrusion and account for, respectively, 46%, 15%, and 15% of the variation of water salinity in the Modaomen channel. The study is featured in not only identifying the major factors in driving seawater intrusion but also quantifying their relative contribution. Thus, the findings are important for water resources manager to predict and manage inland river seawater intrusion in the PRE of China.
... Introduction The topic of water quality is concerning with a major environmental issue as it impacts human life. (He et al., 2008 andChen et al., 2009). One of the significant factors that have an influence on the physical dimensions (such as color) of the water is the characteristics (distribution andconcentration) of fine suspended solids and dissolved matters (Clark et al., 1980). ...
In this study, the empirical approach besides the methods multilinear regression was followed to generate the predictive mathematical models to estimate the water quality parameters values in the surface water of the Shatt Al-arab River which is located southern part
of Iraq. And to show both benefits and the viability of using Landsat 8 optical spectral images to estimate some of the water quality parameters concentration. The daily water quality data archive for the of the total dissolved solids (TDS), conductivity (E.C), Nitrate (NO3), and potential hydrogen ions (pH) of the water in four seasons (winter, spring, summer, and autumn) distributed along three years (2013, 2014, and 2015), was collected from four ground stations along of the Shatt Al-arab River. The objective of the study was to generate seasonal empirical mathematical models for the (open time) that can be used every year, without the need for calibration every time. Optical data were corrected to remove radiometric and atmospheric
error sources effects prior to the developing the models. Multiple regression analysis between measured water quality parameters of the ground stations and the reflectance of the pixels corresponding to the sampling stations was used to generate these models. Determination coefficients (R2) of the proposed mathematical models were between 0.83-0.99. The percentage error between predicted and measured values for these models were between 0.03% -12%. The results of this work indicate the novelty of the approach used to generated these mathematical models for the open time for any year but in the each season. These models are reliable to estimate the spatial and temporal variation of TDS, E.C, NO3, and pH. So models generated from Landsat 8 can be used as a tool to facilitate the environmental, economic, and social management of the surface waters bodies like a Shatt Al-arab River .
... Landsat has collected high-quality and global coverage imagery since the 1970s. It provides a useful collection of satellite imagery for long-term monitoring of earth surface changes, including inland water bodies [21][22][23]. Landsat 5 was launched in 1984 and decommissioned in 2013. It carried two sensors-Multispectral Scanner System (MSS) and Thematic Mapper (TM). ...
Turbidity is an important indicator of riverine conditions, especially in a fragile environment such as the Tibetan Plateau. Remote sensing, with the advantages of large-scale observations, has been widely applied to monitor turbidity change in lakes and rivers; however, few studies have focused on turbidity change of rivers on the Tibetan Plateau. We investigated the pattern of turbidity change in the middle reaches of the Yarlung Zangbo River, southern Tibetan Plateau, based on multispectral satellite imagery and in situ measurements. We developed empirical models from in situ measured water leaving reflectance and turbidity, and applied the best performed s-curve models on satellite imagery from Sentinel-2, Landsat 8, and Landsat 5 to derive turbidity change in 2007–2017. Our results revealed an overall decreasing spatial trend from the upper to lower streams. Seasonal variations were observed with high turbidity from July to September and low turbidity from October to May. Annual turbidity showed a temporally slightly declining trend from 2007 to 2017. The pattern of turbidity change is affected by the confluence of tributaries and the changes in precipitation and vegetation along the river. These findings provide important insights into the responses of riverine turbidity to climate and environmental changes on the Tibetan Plateau.
... El índice de vegetación NDVI mostró ser una variable significante para la modelación de fosfatos. Este índice al ser creado a través de operaciones entre las bandas NIR y rojo del espectro, resalta las propiedades reflectantes de la clorofila (Teta et al., 2017), debido probablemente a su asociación con la materia orgánica permitió obtener una correlación con este nutriente en dichas longitudes de onda (Chen et al., 2009;Para et al., 2010). ...
RESUMEN El inapropiado manejo de las fuentes de agua dulce ha propiciado una crisis poco entendida a escala global. La calidad de agua para uso agronómico implica un problema biogeoquímico que afecta directamente al crecimiento de las plantas, estructura del suelo y propicia la contaminación en los cuerpos de agua. El objetivo de este trabajo fue analizar la concentración espacial de fosfatos dentro de red fluvial de la cuenca Laguna de Bustillos, Chihuahua, México. Se realizaron dos muestreos en la red hídrica de la cuenca con el propósito de calibrar y validar en el entorno espaciotemporal. Para la calibración se levantaron 32 muestras y para la validación 11 muestras. En las muestras se determinó la concentración de fosfatos (PO 4 ³-) mediante un fotómetro de nutrientes. A través de un modelo de regresión lineal múltiple se modelaron las concentraciones de fosfatos en función de variables fisiográficas y las reflectancias puntuales obtenidas de imágenes satelitales en distintas áreas de influencia (250 m, 500 m, 1000 m, 2000 m, 3000 m, 4000 m y 5000 m). La bondad de ajuste se evaluó a través del coeficiente de determinación (R 2) y el error cuadrático medio (ECM). El área de influencia a 2000 m presentó la mayor certidumbre. El modelo de calibración mostró un R 2 de 74.9% y el ECM 1.45 mg L-1 ; en la validación temporal el R 2 fue 78.9% y el ECM, 1.72 mg L-1. El modelo de regresión propuesto resultó ser apto para la predicción de fosfatos en la red hídrica de la cuenca. Los resultados de la modelación son útiles para apoyar la toma de decisiones relacionadas al manejo de nutrientes en la parte agrícola, estrategias de protección en amplias regiones, decisiones sobre futuros monitoreos y evaluaciones de las corrientes que son altamente vulnerables a la degradación ambiental en la cuenca de Bustillos. Palabras Clave: calidad de agua; regresión múltiple; fisiografía; Google Earth Engine; monitoreo ABSTRACT Inappropriate management of freshwater sources has led to a poorly understood crisis on a global scale. The quality of water for agronomic use implies a biogeochemical problem that directly affects the growth of plants, soil structure and promotes contamination in water bodies. The objective of this work was to analyze the spatial concentration of phosphates within the fluvial network of the Laguna de Bustillos basin, Chihuahua, Mexico. Two samplings were carried out in the water network of the basin with the purpose of calibrating and validating in the space-time environment. For the calibration, 32 samples were collected and for the validation 11 samples. In the samples, the phosphate concentration (PO 4 ³-) was determined by means of a nutrient photometer. Through a
... The SSC is typically lower in the offshore area than inside the estuary. However, the trend can be reversed during storm events when waves are strong (Chen et al., 2009). On intra-tidal time scales, the distribution of the SSC depends largely on the resuspension processes. ...
Understanding the transport time scales for sediment in an estuary is important to study the retention of pollutants, such as heavy metals, that adsorb to sediment. In this study, a three-dimensional hydrodynamic and sediment transport model was developed to investigate the transport time scales of sediment in the Modaomen Waterway (MW), China. The results show that approximately 100 and 240 days are required for fine-grained (settling velocity, ωs= 0.2 mm/s) and coarse-grained sediment (ωs = 0.5 mm/s) to transport from the headwater to the estuary mouth, respectively. Unlike dissolved materials, sediment undergoes intermittent settling and resuspension, which are key processes that determine the sediment age. The sediment stays longer at the seabed than suspended in the water column. The sediment has more potential to be eroded from the seabed in the freshwater region because of the strong bottom shear stress. These eroded sediments can be rapidly diffused to the upper water column and advected seaward. In contrast, sediment tends to deposit within the turbidity maximum zone due to low bottom shear stress and weak turbulent mixing. Downstream of the turbidity maximum, turbulent mixing is further suppressed by density stratification and the eroded sediment is rarely diffused to the upper water column. As a result, sediment travels more rapidly in the freshwater region than in the brackish zone. The sediment in the upper water column is mostly advected from upstream, and the difference in the sediment ages near the surface and at the bottom can reach 40 days for the coarse-grained sediment. The sediment age has an effect on water quality because a long sediment retention time facilitates the accumulation of pollutants in the MW.
... Some studies have detected the impact of rainfall on the sediment plume (Chen et al., 2011a,b;Ondrusek et al. 2012). In addition, Chen et al. (2009a) monitored the turbidity change in seawater intrusion reaches of the Pearl River estuary (China). Obviously, extreme weather significantly affects the spatial and temporal variations of suspended sediment, which calls for more attention. ...
... Even when the sampling is completed within a day, the water quality values are not directly comparable from station to station considering variations within the day. While it is critical to monitor the water quality of an area efficiently and effectively, conventional methods of monitoring produce numerical outputs that are too technical that only few people can understand the implications (Chen, 2009). Also given the extensive area of the lake, the limited number of sampling points is not enough to create a visual output that would be easily comprehensible (Khattab and Merkel, 2014). ...
Laguna Lake, the Philippines’ largest freshwater lake, has always been historically, economically, and ecologically significant to the people living near it. However, as it lies at the center of urban development in Metro Manila, it suffers from water quality degradation. Water quality sampling by current field methods is not enough to assess the spatial and temporal variations of water quality in the lake. Regular water quality monitoring is advised, and remote sensing addresses the need for a synchronized and frequent observation and provides an efficient way to obtain bio-optical water quality parameters. Optimization of bio-optical models is done as local parameters change regionally and seasonally, thus requiring calibration. Field spectral measurements and in-situ water quality data taken during simultaneous satellite overpass were used to calibrate the bio-optical modelling tool WASI-2D to get estimates of chlorophyll-a concentration from the corresponding Landsat-8 images. The initial output values for chlorophyll-a concentration, which ranges from 10–40 μg/L, has an RMSE of up to 10 μg/L when compared with in situ data. Further refinements in the initial and constant parameters of the model resulted in an improved chlorophyll-a concentration retrieval from the Landsat-8 images. The outputs provided a chlorophyll-a concentration range from 5–12 μg/L, well within the usual range of measured values in the lake, with an RMSE of 2.28 μg/L compared to in situ data.
... Turbidity is a crucial optical parameter that reveals how clear or transparent the aquatic medium is. It depends, apart from the SPM concentration, on the shape and size distribution of the suspended solids, seawater's refractive index and color components, and various absorption spectra (see Chen et al. 2009). Nevertheless, for a particular location and specific sediment properties, simultaneous measurements of turbidity (using a typical transmissometer) and SPM concentration normally show a quite good correlation, although this is not definite in several cases (Pfannkuche and Schmidt 2003). ...
The potential influence of short-period (May–June 2012) dredging activities (for the installation of a submarine gas pipeline) on physical properties of the marine environment of two shallow-water sites in the Aliveri and Varnavas areas of South Euboean Gulf (Greece) has been evaluated. During the dredging operation in Varnavas, the induced dredge plume traveled up to ~ 750 m from the shoreline, featured by light attenuation coefficient (cp) maxima of 4.01–4.61 m⁻¹ and suspended particulate matter (SPM) concentrations up to 6.01 mg L⁻¹. After dredging the previous parameters reduced to the ambient seawater condition, ~ 0.45 m⁻¹ and < 2.8 mg L⁻¹ on average, respectively. Likewise in Aliveri, the dredging-associated sediment plume drifted offshore up to ~ 400 m from the shoreline, characterized by cp maxima of 2.11–4.86 m⁻¹ and SPM concentrations up to 13.07 mg L⁻¹. After the completion of the excavation and trenching activities, the cp and SPM values were restored to the pre-disturbance condition, ~ 0.6 m⁻¹ and < 2.2 mg L⁻¹ on average, respectively. The migration of the dredge plume in both dredging sites was accomplished through the formation of intermediate and benthic nepheloid layers, whose development and evolution were governed by seawater stratification and flow regime. The dredging-derived SPM levels appeared to increase within a distance of no more than 300 m from the shoreline (near-field zone). Based on data from the literature, this SPM enhancement together with the deposition of a post-dredging residual mud veneer in the near-field zone could deteriorate local marine biota, but in a reversible way.
... The plain of the Pearl River Delta (PRD) is one of the most populous and economically dynamic regions in China, supplying water to 50 million people, but the groundwater in almost half of the area is saline [13,14]. Although water is available, not all of it is suitable for consumption due to groundwater pollution [15] and the continuing saltwater intrusion into the Pearl River Estuary [16]. However, the source of groundwater salinity is a much debated issue. ...
The salinization of groundwater is an issue in coastal areas because it causes the deterioration of freshwater resources, significantly impacting human livelihoods and ecosystems. This study integrated isotopic geochemical measurements with high-throughput sequencing of 16S rRNA gene amplicons to evaluate the source of groundwater salinity and the influence of hydrogeochemical variations on microbial communities under different salinity gradients in the Pearl River Delta of China. Results showed that the groundwater salinity in this area varied from fresh water in the inland area to brackish water, and then to saline water close to the southeast shoreline. The major ions (Na+, K+, Ca2+, Mg2+, Cl−, NO3−, SO42−, and HCO3−) and isotope analyses (2H, 3H, 18O, and 14C) indicated that the groundwater in the confined aquifer was recharged by local precipitation and seawater. A further 14C analysis showed that the salinity of the groundwater was likely attributed to the Holocene transgression. Analysis of the microbial community showed that γ-proteobacteria were frequently observed in all the groundwater samples, while the other main microbial community at class level varied greatly, from β-proteobacteria in the freshwater wells to ε-proteobacteria in the brackish wells and to Bacilli in the saline wells. Exiguobacterium and Acinetobacter were dominant in saline water and the brackish water sample of Q144, while Sulfuricurvum dominated in the brackish water sample of Q143. Aeromonas, no rank Gallionellaceae, no rank Methylophilaceae, Acidovorax, and Comamonas unevenly thrived in the freshwater samples collected from different locations. Therefore, the distribution of microbial communities reflected the salinity and hydrogeochemical characteristics of a groundwater aquifer, and can be regarded as a potential environmental indicator in the groundwater.
... El avance actual en imágenes hiperespectrales, con la capacidad de registrar simultáneamente hasta 200 canales espectrales, son los más recomendables para la detección de parámetros hídricos (Olmanson et al., 2013;Chen, Xiao y Li, 2016), Son numerosos los estudios en los que se han determinado parámetros relativos a la calidad del agua en superficies marinas, como la clorofila, fitoplancton, materia orgánica disuelta, sólidos disueltos en suspensión o turbidez. Por lo que, la utilización de rangos espectrales desde el visible al infrarrojo cercano, información donde gran parte la energía es absorbida, han demostrado su utilidad para determinar datos sobre la calidad del agua (Giardiano et al., 2001;Kloiber et al., 2000;Bustamante et al., 2009;Chen et al., 2009;Fichot et al., 2016). Otros trabajos recientes, se centran en analizar mediante técnicas de teledetección parámetros de la calidad del agua en aguas interiores. ...
The Basin of Conchos River, located in the State of Chihuahua (Mexico), has suffered a marked deterioration due to the development of human activities. The urban population growth, industrialization, and agriculture have significantly degraded water resources of this basin. To examine the quality of its waters, the reservoirs of Las Vírgenes dam, the Colina lake, and La Boquilla dam have been analyzed, determining the parameters of dissolved oxygen, pH, nitrates, total dissolved solids, turbidity and temperature from water. Samples. Using these data and the spectral information of Landsat 5 satellite images, 30 linear regression models were evaluated; from these models, turbidity obtained the best match. The regions of spectrum 0.52-0.6 μm and 0.63-0.69 μm, provided by the predictor variable, appeared as the ranges of higher correlation with the values of turbidity. The model used to represent the turbidity spatially distributed shows that La Boquilla dam gets the highest values related to the suspension of sediments provided by ephemeral channels throughout the reservoir.
... The plain of the Pearl River Delta (PRD) in China is responsible for the water supply of 50 million people, but the groundwater is contaminated due to high salinity and pollution [22][23][24] , as well as continuous seawater intrusion into the Pearl River Estuary 25 . The groundwater salinity is relatively stable in most areas of the PRD, since it primarily originated from paleo-seawater 26,27 due to the Holocene transgression 28 . ...
Abstract Almost half of the groundwater in the Pearl River Delta (PRD) contains salt water originally derived from paleo-seawater due to the Holocene transgression, which then generates intense physicochemical gradients in the mixing zone between freshwater and saltwater. Although some studies have been conducted on the hydrological and geochemical characteristics of groundwater in the PRD to monitor the intrusion of seawater, little attention has been paid to the microbial community of this particular region. In this study, we implemented a high-throughput sequencing analysis to characterize the microbial communities along a salinity gradient in the PRD aquifer, China. Our results indicated that the microbial community composition varied significantly depending on the salinity of the aquifer. The presence of abundant anaerobic microorganisms of the genera Desulfovibrio and Methanococcus in certain saltwater samples may be responsible for the gas generation of H2S and CH4 in the stratum. In saline water samples (TDS > 10 g/L), the linear discriminant analysis effect size (LEfSe) analysis found two biomarkers that usually live in marine environments, and the aquifers of the PRD still contained large quantity of saltwater, indicating that the impact of the paleo-seawater has lasted to this day. The predictive metagenomic analysis revealed that the metabolic pathways present in the groundwater samples studied, included the degradation of pesticides and refractory organics (dichlorodiphenyltrichloroethane (DDT), atrazine and polycyclic aromatic hydrocarbons), matter cycling (methane, nitrogen and sulfur), and inorganic ion and mineral metabolites. This study can help enhance our understanding of the composition of the microbial assemblages and its implications as an environmental indicator in an aquifer affected by saltwater intrusion.
... MODIS data also used in study (Guzman and Santaella 2009) to calculate concentration of suspended sediment in Mayaguez Bay (Puerto Rico). Chen et al. have used EO-ALI satellite imagery and found negative regression model between water turbidity in the Pearl River Estuary and reflectance at 570 nm (Chen et al. 2009). ...
The traditional methods for measuring water quality variables are timeconsuming and do not give a synoptic view of a water body or, more significantly, a synoptic view of different water bodies across the landscape. However, remote sensing technology with advantages such as wide area coverage and short revisit interval have been effectively used for environmental pollution applications, such as for monitoring water quality parameters. Many studies around the world show that optical satellite imagery can be used effectively in evaluating suspended sediment concentration. This article presents results of monitoring suspended sediment concentration in Red River, Hanoi, Vietnam through ground truth measurements and VNREDSat-1A multispectral data. The results obtained in the study can be used to serve the management, monitoring and evaluation of surface water quality.
... Landsat5 TM and ETM+ band 3 (630 -690 nm) were used to map turbidity (1.5 -8 NTU) in the Guadalquivir River (Spain) (Bustamante et al. 2009). Chen et al. (2009a) suggested using a green band (Band 4) of a hyperspectral sensor, EO-1 ALI, to estimate water turbidity (5 -16 NTU) in the Pearl River Estuary (China). A regional turbidity algorithm using MODIS-Aqua 250-m red band was proposed in the Adour River plume (Bay of Biscay, France), where field turbidity values varied between 0.5 and 70 NTU (Petus et al. 2010). ...
Water quality is examined in two contrasting estuaries, Barataria Bay and Apalachicola Bay, in the northern Gulf of Mexico (NGOM) using in situ and satellite observations. The two estuaries considered in this study are unique - Barataria Bay represents a sediment-starved degrading system while Apalachicola Bay, a naturally intact system, is threatened by a two decade long tri-state water distribution conflict. The present state of water quality parameters, their controlling processes, and distributions are largely limited due to scarcity of synoptic measurements in these estuaries. In this study, a Landsat-based band-ratio algorithm is presented first to examine spatial variability of CDOM abundance during major forcing events in Barataria Bay. The results show that the meteorological and hydrological forcings tend to disrupt general trends of CDOM in spring and winter when the bay experiences elevated Mississippi River discharge and the passages of cold fronts. The idea of using a band-ratio algorithm is extended further to study CDOM dynamics, for the first-time using VIIRS sensor, in Apalachicola Bay. With conservative CDOM-DOC relationships, NCOM-based surface currents, and empirically-derived CDOM maps, DOC export fluxes are estimated which represent ~7% and ~21% of the 110-year mean spring and fall exports for the Mississippi River. A 7-year time-series of turbidity and Landsat imagery are used to demonstrate a simple but robust technique to monitor turbidity in Apalachicola Bay. Seasonal turbidity maps indicate distinct patterns of moderate to high turbid waters in spring and winter, and low to moderately turbid waters in summer and fall. Water quality monitoring strategy presented in this study supports the US EPA’s Clean Water Act to protect human-health and the environment. The empirical relationships presented in earlier chapters of this dissertation are limited to specific areas; a VIIRS-based tuned quasi-analytical algorithm (QAA-V) is additionally presented to monitor water inherent optical properties (IOPs) in different estuaries in the NGOM. As IOPs are directly associated to the abundance of water constituents, QAA-V can provide a useful tool for regional, state, and federal agencies to monitor water quality for making decisions concerning strategies and plans to mitigate environmental problems.
... where a′ g (λ) is the uncorrected CDOM absorption coefficient at wavelength λ; a g (λ) is the modified absorption coefficient that has been corrected for scattering; D(λ) is the optical density at wavelength λ; and l is the cuvette light path length in meters (0.1 m in this study). The absorption coefficients at wavelength 355 nm (a g (355)), 400 nm (a g (400)) and 440 nm (a g (440)) were usually chosen to express the concentration of CDOM (Chen et al., 2009;Griffin et al., 2011;Hong et al., 2005;Zhang et al., 2007;Zhu et al., 2014). In this study, a g (355), a g (400) and a g (440) were selected for further analyses. ...
Keywords: Chromophoric dissolved organic matter (CDOM) Field measured water reflectance Retrieval model Sentinel-2MSI Landsat-8 OLI Poyang Lake A B S T R A C T Chromophoric dissolved organic matter (CDOM), the key component in aquatic environment, plays an important role in biogeochemical processing. In this study, in situ reflectance and water samples were used to develop models for estimating CDOM absorption in a complex freshwater environment in Poyang Lake, China. The in situ water reflectance spectra, CDOM absorption spectra and other watercolor parameters from 92 samples collected in four representative study areas between 2015 and 2016 were analysed. Band ratio models were established to estimate CDOM absorption coefficient at 355 nm [a g (355)] based on the correlation analysis between reflectance and a g (355). The results indicated that the models performed well for estimating a g (355) when the 92 samples were divided into two datasets with the threshold of concentration of total suspended matter (TSM) as 10 mg/L. The band ratios of R(689)/R(497) and R(767)/R(826) were selected to establish models for retrieval of a g (355) in clean water (TSM < 10 mg/L) and turbid water (TSM ≥ 10 mg/L), respectively. The determination coefficients (r 2) of calibration models for clean and turbid water were 0.70 and 0.73, respectively. The percentage root-mean-square errors (%RSME) of validation models for clean and turbid water were 13.2% and 11.6%, respectively. The simulated Sentinel-2 and Landsat-8 bands based on reflectance spectra were used to examine potential capability for retrieving CDOM using these sensors. The results indicated that Sentinel-2 performed better than Landsat-8 for estimating a g (355). The Sentinel-2 band ratio of B4/B2 or B5/B2 and B7/B8 or B7/B8A are effective for retrieval of CDOM in clean and turbid water of Poyang Lake, respectively.
... Most of them deal with reservoirs, estuaries and seas. Experiments in the estuary of the Pearl River (China) (Chen et al. 2009) found negative regression model between water turbidity and reflectance at 570 nm (maximum correlation spectral band between 350 and 2500 nm) R 570. The best fit relationship was where T, R 570 are the degree of turbidity (in Nephelometric Turbidity Unit, NTU), surface water reflectance at 570 nm, respectively. ...
Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP-7 Marie Curie-International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;-Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking field-based methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses. ENVIRONMENT 44 KEY wORDS: sediment budget, suspended sediment, erosion processes, erosion modeling CITATION:
... A recent study by Abdelmalik (2016) used the ASTER data to monitor water quality parameters such as temperature, turbidity, pH, salinity, TDS, conductivity, TOC, and ortho-phosphorus. Satellite remote sensing could also be used to determine nutrient distributions in lakes with reasonable confidence (El Saadi et al. 2014;Chen et al. 2009;Volpe et al. 2011). Images from Hyperspectral Imager for the Coastal Ocean (HICO) on the International Space Station (ISS) were employed to derive chl-a, CDOM absorption, and turbidity in northern Florida. ...
Recent advancements in the field of remote sensing and geographic information systems (GIS) have made it possible to conduct large-scale water remediation studies. Using improved spectral and spatial resolution sensors and geospatial modeling techniques, water quality parameters such as chlorophyll-a, algae bloom, turbidity, suspended sediments, and mineral content in water bodies including groundwater are being monitored at low cost and with greater accuracy. Integration of these technologies with field monitoring have successfully aided in identification of contamination zones and sources of contamination, and for developing strategies for remediation. High-resolution mapping of contamination zones will further help in allocating remediation efforts to the critically affected areas. This chapter investigates the status of ongoing research in the domain of remote sensing and GIS for water quality monitoring and management, and remediation of water resources.
... The Pearl River in southern China is the third largest river in China in terms of drainage basin area (Fig. 2), and its delta is the world's largest urban area in both size and population (World Bank, 2016). Frequent saltwater intrusion has occurred in recent years, and poses a threat to water supply in the delta ( Chen et al., 2009). In a previous study, we found that dry season rainfall and discharge are likely to reduce throughout the basin in the future due to climate change ( Yan et al., 2016). ...
Water allocation is facing profound challenges due to climate change uncertainties. To identify adaptive water allocation strategies that are robust to climate change uncertainties, a model framework combining many-objective robust decision making and biophysical modeling is developed for large rivers. The framework was applied to the Pearl River basin (PRB), China where sufficient flow to the delta is required to reduce saltwater intrusion in the dry season. Before identifying and assessing robust water allocation plans for the future, the performance of ten state-of-the-art MOEAs (multi-objective evolutionary algorithms) is evaluated for the water allocation problem in the PRB. The Borg multi-objective evolutionary algorithm (Borg MOEA), which is a self-adaptive optimization algorithm, has the best performance during the historical periods. Therefore it is selected to generate new water allocation plans for the future (2079-2099). This study shows that robust decision making using carefully selected MOEAs can help limit saltwater intrusion in the Pearl River Delta. However, the framework could perform poorly due to larger than expected climate change impacts on water availability. Results also show that subjective design choices from the researchers and/or water managers could potentially affect the ability of the model framework, and cause the most robust water allocation plans to fail under future climate change. Developing robust allocation plans in a river basin suffering from increasing water shortage requires the researchers and water managers to well characterize future climate change of the study regions and vulnerabilities of their tools.
... Water quality is an extremely important environmental factor as it affects human beings and their economic activities (e.g. Chen et al., 2009 andHe et al., 2008). The major factor that affects the physical aspect (such as color) of the water is the concentration and distribution of fine suspended components and dissolved matter (Clark et al., 1980). ...
Understanding the statistical relations among the Advanced Space borne Thermal Emission and Reflection Radiation (ASTER) data and observed water quality parameters, in order to develop a mathematical relation for the precise prediction of the missing data in a given area, is the main aim of the present study. This should enable to establish a spatial distribution map for each parameter of water quality for the area. The method was applied to Qaroun Lake in the Fayoum depression of Egypt. The water quality parameters obtained from ASTER data used in the present work are: Temperature, Turbidity, Hydrogen ion concentration (pH), Salinity, Total Dissolved Solids (TDS), Electrical Conductivity (EC), Total alkalinity, Total Organic Carbon (TOC) and Ortho-phosphorus. 18 water sample data were used in the study: 15 sample data for mathematical model construction, giving the relation between the ASTER values and the water quality parameters, while 3 samples data were used to test the obtained model. The SPSS software of IBM was also used in the present research for the applied statistical analysis. The analysis showed a significant correlation between the observed values and the remotely sensed data with R² > 0.94 and sig. < 0.01 in most cases. The calculated values resulting through the obtained equation showed a high accuracy: Root mean square error (RMSE) ranging from 0.8 to 0.014 and Standard Estimated Error (SEE) ranging from 0.9 to 0.0116. ERDAS Imagine and ArcGIS packages were used for applying the obtained mathematical model and spatial distribution map to the Qaroun Lake. © 2016 National Authority for Remote Sensing and Space Sciences
... Therefore, land-and cloud-oriented MODIS data were selected in this study. Several previous studies have also used different remote-sensing images to study C TSM and its dynamic distribution in Deep Bay and its adjacent water, the PRE (Chen et al. 2005Chen et al. , 2009 Tang et al. 2009; Tian et al. 2014; Xi, Zhang, and Chen 2008). According to the previous study in Deep Bay and the PRE, the bands often used for C TSM retrieval are at 550–700 nm (Tian et al. 2014). ...
... From the above analysis, TSS retrieval models based on other broadband satellite data such as MODIS were referred to the study. The model has been successful applied in Tampa Bay, USA [8], in Modaomen waterway, Pearl River, China [9], in Apalachicola Bay, USA [3,[10][11][12] and in estuary of Yangtze River and Xunwen Coral Reef Protection Zone [1]. The same trait of the models is that the relationship of the ratio of logarithmic transformation of red band and near infrared band and logarithmic transformation of TSS concentration was considered fully. ...
Based on 119 in-situ data from five estuaries and coasts of South China including Xunwen coast, estuary of Moyangjiang River, estuary and coast of Pearl River, estuary of Hanjiang River and estuary of Yangtze River, this paper aims to develop and establish a TSS retrieval model that applicable in different field conditions. After recalibrating and validating the form with the highest correlation coefficient between reflectance and TSS concentration and other TSS retrieval models that have been successful applied in many places, we found that the quadratic model of the ratio of logarithmic transformation of red band and near infrared band and logarithmic transformation of TSS concentration (QRLTSS) shows the highest performance. QRLTSS model based on Landsat OLI, ETM+ and TM can explained about 71% of the TSS concentration variation (4.3∼577.2 mg/L) in the five regions and has a high and acceptable validation accuracy with root mean square error (RMSE) of 21.5–25mg/L and mean relative error (MRE) of 27.2–32.2%. We concluded that QRLTSS model can be used to quantify the TSS concentration of multiple estuaries and coasts of south China which would be helpful to understand the temporal and spatial variation of TSS in a large region. QRLTSS model should be applied to Landsat imagery for further validation in the future. The approach proposed in the paper also could promote the research work of establishing regional and uniform TSS retrieval model forward.
... Therefore, land-and cloud-oriented MODIS data were selected in this study. Several previous studies have also used different remote-sensing images to study C TSM and its dynamic distribution in Deep Bay and its adjacent water, the PRE ( Chen et al. 2005Chen et al. , 2009Tang et al. 2009;Tian et al. 2014;Xi, Zhang, and Chen 2008). According to the previous study in Deep Bay and the PRE, the bands often used for C TSM retrieval are at 550-700 nm ( Tian et al. 2014). ...
This study proposed a method for developing high spatial resolution Gaofen-1 satellite (GF-1) Wide Field Imager (WFI)-based total suspended matter concentration (CTSM) retrieval model with the assistance of Moderate Resolution Imaging Spectroradiometer (MODIS) data, using the Deep Bay in China as a case. Based on long-term calibrated CTSM measurements of optical backscatter (OBS) 3A turbidity and temperature monitoring system of two stationary stations from January 2007 through November 2008, 33 match-ups were selected to build an exponential retrieval model for MODIS atmospherically corrected remote-sensing reflectance (Rrs) ratio (Rrs,645/Rrs,555). Validation of the MODIS model showed well agreement with the seven in situ CTSM measurements with a root mean squared error (RMSE) of 5.06 mg l−1 and a coefficient of determination R2 of 0.80. Aided with six MODIS retrieved CTSM products, different band combinations (single band (Rrc,660), band subtraction (Rrc,660–Rrc,560), band ratio (Rrc,660/Rrc,560), and total suspended matter index at 660 nm band (TSMI660) were evaluated for simultaneous GF-1 WFI Rayleigh-corrected reflectance (Rrc). The results showed that the exponential model based on the Rayleigh-corrected reflectance ratio (Rrc,660/Rrc,560) could achieve acceptable accuracy, with RMSE of 14.80 mg l−1 and R2 of 0.62. The proposed method would be helpful for dynamic monitoring in the Deep Bay, and more important could also provide an alternative approach for studies when in situ measurements are unreachable.
... As reported in most research and remote sensing studies, turbidity is directly proportional to the DN or reflectance. However, in the present study, turbidity is increasing with reduction in DN indicating the presence of suspended and colloidal organic matters in the creek which absorb reflectance and decrease the DN value (Chen et al. 2009;Satapathy et al. 2010;Borges et al. 2011). A negative relationship in the green and red bands indicates that the study of water quality parameters is conducive in both these bands. ...
Today object-based image analysis provides an option for integrating spatial information beyond the conventional pixel based classifications for high resolution imagery. Due to its rare applicability in pollution assessment, an attempt has been made to assess the spatial extent of sewage pollution in Malad Creek, Mumbai, India. Based on multi-resolution segmentation of IRS P6 (LISS IV) image and Normalized Difference Turbidity Index (NDTI), the various water quality regions in the creek were classified. The existing literature implies that the reflectance of turbid water is similar to that of bare soil which gives positive NDTI values. In contrast to this, negative values of NDTI are observed in the present study due to the presence of organic matter which absorbs light and imparts turbidity; which is supported by the significant correlation between NDTI and turbidity. A strong relationship is observed between turbidity and water quality parameters implying the impact of organic matter through discharges of sewage in the creek. Based on the classified regions and the water quality parameters, the extent of pollution was ranked as high, moderate, low and least. The methodology developed in the present study was successfully applied on an IKONOS image for the same study area but a different time frame. The approach will help in impact assessment of sewage pollution and its spatial extent in other waterbodies.
... Space-borne remote sensing has become a potential data source to model land and water resource systems. Various remotely sensed image-based tools are also developed to measure turbidity (Chen et al. 2007(Chen et al. , 2009Shen et al. 2010), suspended sediment concentration (Jiang et al. 2009;Nechad et al. 2010;Onderka et al. 2011), chlorophyll a (Fiorani et al. 2006;Wang et al. 2010), phytoplankton (Kwiatkowska and McClain 2009), cyanobacterial blooms (Kutser et al. 2006), and other physical water quality parameters (Liu et al. 2003;Hu et al. 2004). Using these data in hydrologic modeling requires an understanding of the potentials and limitations of the data sets. ...
In most developing
countries
, there is a lack of historical sediment data. In Ethiopia, over the past 40 years, sediment concentrations in rivers are periodically measured for determining sediment rating curves. But, no such historical data are available for lakes such as Lake Tana
in Upper Blue Nile River basin
, greatly hampering the ability to track the trend of environmental pollution. The objective of this study is to determine whether models can be used to estimate the historical record of lake sediment
concentrations. In this study, a relationship between reflectance
and TSS was developed and 10-year TSS time series data were generated from MODIS
/Terra images. The 10-year TSS time series data were used to calibrate and validate an erosion model. The soil and water assessment tool variable source area (SWAT-VSA)
model was selected because it has performed well in the Lake Tana basin. The result showed that at monthly timescale, TSS at the river mouth can be replicated with Nash–Sutcliffe efficiency (NS) of 0.34 for calibration and 0.21 for validation periods. Percent bias (PBIAS) and ratio of root mean square error (RSR) to the standard deviation of measured data are all within range. Given the inaccessibility and costliness to measure TSS at river mouths to a lake, the results found here are considered best estimates for suspended sediment budget in water bodies of the basin. However, direct measurement or improved models should yield better results.
... Mainly passive sensors are employed to assess water quality, clarity, and turbidity in related studies, including Landsat (Olmanson et al. 2008;Zhao et al. 2011;Kabbara et al. 2008), Earth Observing 1 (EO-1) ALI (Chen et al. 2009), and SeaWiFS (Chen et al. 2007). As a characteristic example, a 20-year archive of Landsat data was effective in providing correlations with field-measured secchi disk depths (SDD) up to R 2 ¼ 0:96, to characterize water clarity in Minnesota lakes, USA (Olmanson et al. 2008). ...
Recognizing the imperative need for biodiversity protection, the convention on biological diversity (CBD) has recently established new targets towards 2020, the so-called Aichi targets, and updated proposed sets of indicators to quantitatively monitor the progress towards these targets. Remote sensing has been increasingly contributing to timely, accurate, and cost-effective assessment of biodiversity-related characteristics and functions during the last years. However, most relevant studies constitute individual research efforts, rarely related with the extraction of widely adopted CBD biodiversity indicators. Furthermore, systematic operational use of remote sensing data by managing authorities has still been limited. In this study, the Aichi targets and the related CBD indicators whose monitoring can be facilitated by remote sensing are identified. For each headline indicator a number of recent remote sensing approaches able for the extraction of related properties are reviewed. Methods cover a wide range of fields, including: habitat extent and condition monitoring; species distribution; pressures from unsustainable management, pollution and climate change; ecosystem service monitoring; and conservation status assessment of protected areas. The advantages and limitations of different remote sensing data and algorithms are discussed. Sorting of the methods based on their reported accuracies is attempted, when possible. The extensive literature survey aims at reviewing highly performing methods that can be used for large-area, effective, and timely biodiversity assessment, to encourage the more systematic use of remote sensing solutions in monitoring progress towards the Aichi targets, and to decrease the gaps between the remote sensing and management communities.
... Satapathy and associates (2010) found that that turbidity was positively correlated with reflectance as far as coast and seashore zones are concerned, which is consistent with many other case studies too. But in the present case of Malad, for creek and drains entering the creek zone, a strong negative correlation was found between turbidity and reflectance because of presence of high organic matter (Chen et al., 2009) which is evident from the biochemical oxygen demand (BOD) values that range from 15-25 mg/L and 156 -260 mg/L in drains numerous random due to discharges of sewage and wastewater. Water quality in terms of turbidity is estimated at locations other than the in situ sampling locations by means of reflectance of satellite imagery using derived equations based on least square method. ...
The water quality of Malad Creek in Mumbai is deteriorating due to heavy discharge of partially treated wastewater and sewage from point and non-point sources. Assessing environmental condition on a large scale requires lot of efforts, is more time consuming and can sometimes also be uneconomical. In the present study, an attempt has been made to retrieve a water quality parameter and assess the extent of sewage pollution through remote sensing image of IKONOS. For in-situ measurement, locations were identified using global positioning system and water samples from creek and drains were collected and analysed for turbidity and BOD. To study the influence of sewage and wastewater on creek, a linear correlation was established between turbidity and reflectance of visible bands of the image. A strong negative correlation, from 0.72 to 0.98, was observed between turbidity and reflectance values at creek and drain locations. This was due to high organic content, observed as BOD, in the water. Further, equations were formulated based on least square method for estimating turbidity at unknown locations to know the extent of pollution in the creek environment.
... Space-borne remote sensing has become a potential data source to model land and water resource systems. Various remotely-sensed images based tools are also developed to measure turbidity (Chen et al., 2007(Chen et al., , 2009Shen et al., 2010), suspended sediment concentration (Jiang et al., 2009;Nechad et al., 2010), chlorophyll-a (Fiorani et al., 2006;Wang et al., 2010), phytoplankton (Kwiatkowska and McClain, 2009), cyanobacterial blooms (Kutser, 2009) and other physical water quality parameters (Hu et al., 2004;Liu et al., 2003). Using these data in hydrologic modeling requires an understanding of the potentials and limitations of the data sets. ...
... retrieving water constituents (Chen et al., 2007; Doxaran et al., 91 2009; Hu et al., 2004; Miller and McKee, 2004), among which 92 MODIS has a unique advantage in ocean color remote sensing with 93 its twice daily coverage and 250 m spatial resolutions for dynamic 94 coast or lake sediment movement. Such advantages have been 95 explored in many studies (e.g., Hu et al., 2004; Miller and Mckee, 96 2004; Liu et al., 2006; Sipelgas et al., 2006; Kutser et al., 2007; 97 Liu and Rossiter, 2008; Wu and Cui, 2008; Chen et al., 2009a,b; 98 Jiang et al., 2009; Tarrant et al., 2010; Wang et al., 2010a,b; Wang 99 and Lu, 2010; Zhang et al., 2010a,b; Chen et al., 2011a,b; Jiang and 100 Liu, 2011; Zhao et al., 2011; Binding et al., 2012; Feng et al., 2012; 101 Ondrusek et al., 2012; Wu et al., 2013a,b). 102 Many MODIS-related models have been developed for retriev- 103 ing TSS using analytic, semi-analytic or empirical algorithms. ...
The objective of this study was to evaluate the performance of moderate resolution imaging spectroradiometer (MODIS) 250 m based TSS (Total Suspended Solids) retrieval model for developing the model of wide-range TSS concentrations. Using field spectral and TSS data (5.8–577.2 mg/l) collected from estuary and coast of China, we calibrated (N = 40) and validated (N = 20) the 6 TSS retrieval models in forms of single band (B1 or B2), difference of the two bands, sediment index, band ratio and log-ratio by the least-squares technique. Results showed that the quadratic model of log-ratio is of the best accuracy (Calibration: R 2 = 0.752, N = 40. Validation: TSS > 31 mg/l, RMSE = 37.9 mg/l, N = 12; TSS⩽31mg/l, RMSE = 3.25 mg/l, N = 8). We also found that the spectral log-ratio values increased with the increasing of TSS when TSS < 31 mg/l, but decreased with increasing TSS when TSS > 31 mg/l. The findings of quadratic curve vertex (log-ratio: ∼1.58) in the proposed TSS model indicated that the spectral log-ratio may be sensitive to TSS of both low and high concentrations. We further applied the preferred model to retrieve TSS concentration from the MODIS 250-m images in turbid estuarial and clear coastal waters, and obtained a good mapping accuracy from the result (TSS > 31 mg/l: RMSE = 38.6 mg/l, MRE = 24.7%, N = 17; TSS⩽31mg/l: RMSE = 2.1 mg/l, MRE = 19.5%, N = 11). The vertex-based methodology of TSS model developed in the study is applicable in mapping TSS concentrations that are of a wide range variation in estuarine and coastal water bodies based on MODIS 250-m image, and as well to maximize its application potential due to high imaging frequency (two times during daytime) and appropriate space resolution of MODIS images. Therefore, the method can be used to detect the high temporal variability of TSS during tidal cycle. As such, the application of MODIS-water quality detection technology can be extended to coastal sediment movement.
The mixing processes of fresh-salt water in estuarine and coastal regions have a substantial impact on the characteristics of heavy metals. A study was conducted in the Pearl River Estuary (PRE), located in South China, to examine the distribution and partitioning of heavy metals and the factors that influence their presence. Results showed that the hydrodynamic force, caused by the landward intrusion of the salt wedge, was the major contributor to the aggregation of heavy metals in the northern and western PRE. Conversely, metals were diffused seaward at lower concentrations along the plume flow in surface water. The study found that some metals, including Fe, Mn, Zn and Pb, were significantly higher in surface water than in bottom water in eastern waters, but the reverse was true in the southern offshore area, where limited mixing hindered the vertical transfer of metals in the water column. The partitioning coefficients (KD) of metals varied, with Fe exhibiting the highest KD (1038 ± 1093 L/g), followed by Zn (579 ± 482 L/g) and Mn (216 ± 224). The highest KD values of metals in surface water were observed in the west coast, while the highest KD in bottom water was found in eastern areas. Furthermore, re-suspension of sediment and the mixing of seawater and freshwater offshore, caused by seawater intrusion, resulted in the partitioning of Cu, Ni and Zn towards particulate phases in offshore waters. This study provides valuable insights into the migration and transformation of heavy metals in dynamic estuaries influenced by the interaction of freshwater and saltwater and highlights the importance of continued research in this field.
Effects of Mineral Elements on the Environment
The occurrence of black-odorous water (BOW) in urban waters is a common problem in China that has occasional, seasonal, and perennial rules. The treatment of urban has become an important task for water managers in China. Based on field BOW spectra and 13 types of water quality parameters measured in Shenzhen City, in this study, we processed three types of spectra, including normalized, difference, and ratio spectra, to reveal the correlation between the spectra and the water quality parameters, especially for the spectra and four indicators that are used to distinguish BOW. The four indicators include Secchi depth (SD), dissolved oxygen (DO), oxidation-reduction potential (ORP), and ammonia nitrogen (NH3-N). Furthermore, we analysed the spectral sensitivity of the different water quality parameters to build a quantitative regression model between the water quality parameters and the portrait spectrum. The results showed the following: (1) Of the four indicators, both SD and NH3-N were significantly related to the spectrum of mild and severe BOW, and the ORP was only significantly related to the spectrum of severe BOW. The correlation between DO and BOW was not significant. (2) For mild BOW, the sensitive bands were 404 to 572 nm and 704 to 864 nm for the SD and 705 to 717 nm for NH3-N. For severe BOW, they were 499 to 606 nm and 730 to 900 nm for the SD, 556 to 664 nm for NH3-N, and 642 to 709 nm for the ORP. (3) The SD had the strongest correlation with the BOW spectrum. The correlation between the SD and the BOW spectrum was symmetrically distributed in the range of 404 to 572 nm near 489 nm, whereas 545 nm appeared as the centre in the range of 499 to 606 nm. (4) The best regression relationship between the SD and BOW was R 489/ R 714 (coefficient of determination R ² = 0.8806) and R 545 (R ² = 0.4868) for the mild and severe grades, respectively. The best regression relationship was R 489- R 607 (R ² = 0.7598) between NH3-N and mild BOW. The results of this study provide important guidance significance and application value regarding the selection of bands, model construction, and result verification for urban BOW using remote sensing.
Retrieving total suspended solids (TSS) concentration accurately is essential for sustainable management of estuaries and coasts, which plays a key role in the interaction between hydrosphere, pedosphere and atmosphere. Although many TSS retrieval models have been published, the general inversion method that is applicable to different field conditions is still under research. In order to obtain a TSS remote sensing model that is suitable for estimating TSS concentrations with wide range in estuaries and coasts by Landsat imagery, after reviewing a number of Landsat-based TSS retrieval models and improving a comparatively better one among them, this study developed a quadratic model using the ratio of logarithmic transformation of red band and near-infrared band and logarithmic transformation of TSS concentration (QRLTSS) based on 119 in situ samples collected in 2006–2013 from five regions of China. It was found that the QRLTSS model works well and shows a satisfactory performance. The QRLTSS model based on Landsat TM (Thematic Mapper), ETM+ (Enhanced Thematic Mapper Plus) and OLI (Operational Land Imager) sensors explained about 72 % of the TSS concentration variation (TSS: 4.3–577.2 mg L−1, N = 84, P value
This study aimed to develop a reliable turbidity model to assess reservoir turbidity based on Landsat-8 satellite imagery. Models were established by multiple linear regression (MLR) and gene-expression programming (GEP) algorithms. Totally 55 and 18 measured turbidity data from Tseng-Wen and Nan-Hwa reservoir paired and screened with satellite imagery. Finally, MLR and GEP were applied to simulated 13 turbid water data for critical turbidity assessment. The coefficient of determination (R2), root mean squared error (RMSE), and relative RMSE (R-RMSE) calculated for model performance evaluation. The result show that, in model development, MLR and GEP shows a similar consequent. However, in model testing, the R2, RMSE, and R-RMSE of MLR and GEP are 0.7277 and 0.8278, 0.7248 NTU and 0.5815 NTU, 22.26% and 17.86%, respectively. Accuracy assessment result shows that GEP is more reasonable than MLR, even in critical turbidity situation, GEP is more convincible. In the model performance evaluation, MLR and GEP are normal and good level, in critical turbidity condition, GEP even belongs to outstanding level. These results exhibit GEP denotes rationality and with relatively good applicability for turbidity simulation. From this study, one can conclude that GEP is suitable for turbidity modeling and is accurate enough for reservoir turbidity estimation.
Sedimentation in reservoir is a common problem in any multipurpose river valley project and is effective upon the performance of it. Every dam has an estimated volume of water holding capacity at the time of inception, but it gradually reduces by siltation. The presence of sediments in water causes turbidity and it slowly precipitates on the floor of the reservoir. Normalized difference turbidity index (NDTI) is a remote sensing technique widely used to identify the water turbidity, which is the ratio of red and green bands of solar spectrum. In Panchet Dam actual rate of siltation exceeds the assumed rate that fills up the entire reservoir area at a faster rate. In this situation, the study has been conducted to explain the variation of water turbidity of the dam throughout the year 2015. Major findings of the study indicate that the turbidity level jumps from 60 NTU to 700 NTU in the monsoon. High turbid water covers 50.57%, 64.22% and 52.79% area of the reservoir in July, August and September, respectively. In contrast, coverage of low turbid water is more than 71.68% in the months of February and June. The medium turbid water covers less than 35.82% area throughout the year except the months of September and October. High level of correlation exists (R² = 0.900) between NDTI values and total suspended sediments concentration in mg/L (N = 15, p < 0.05) with minimal RMSE (13.59). Variation of seasonal turbidity and different types of turbidity are significant at 95% (p < 0.05) level of significance. The paper is an attempt to probe into the seasonal variation of water turbidity of the dam with the application of NDTI method and related statistical measures.
Mouth bars are important morphological units in deltaic and estuarine systems, which have encountered with significant topography variations driven by anthropogenic interferences and natural forcings. On the basis of seven selected maritime charts covering from 1960s to 2016, we focus on the morphological evolution of mouth bar with bifurcating channels in the Modaomen Estuary, the main fluvially-dominated estuary of the Pearl River Delta. The bar area is relatively in equilibrium with barely aggregation and degradation before 1990 while overall erosion was found thereafter. Sediment volume of the mouth bar between the −2 m and −7 m isobaths drastically decreased after 1990s. Correspondingly, the area of −4 m isobaths of the bar stepwise decreased from about 18 × 10⁶ m² to 2 × 10⁶ m², indicating the body of mouth bar above −4 m almost disappeared. The two side channels also suffered significantly morphological evolution. The West Channel (WC) was subjected to uninterrupted erosion. Especially during 2000–2005, the WC below the −2 m isobath experienced remarkable erosion with the increment of water volume reaching 6.7 × 10⁶ m³. The East Channel (EC) had the potential to expand seaward between 2000 and 2011 yet encountered with accumulation after 2011. Meanwhile, the thalweg of the EC seemed hard to distinguish and the WC displayed more meandering thalweg. Furthermore, Empirical Orthogonal Function was applied to quantify the bathymetric changes with independent modes. The temporal variations of fluvial sediment input displayed significant decreasing trend at MK from 1960 to 2014, which presented a statistically significant relationship with the third mode. However, it only accounts for 13.4% of the overall evolution patterns. Although the remarkable reduction of sediment input generally associates with the degradation in bar area, the sediment load is probably not the primary mechanisms driving morphological changes in the Modaomen Estuary. Anthropogenic interferences including large-scale reclamation and intensive sand excavation should be responsible for the morphological changes.
Recently, the marine habitat has been under pollution threat, which impacts many human activities as well as human life. Increasing concerns about pollution levels in the oceans and coastal regions have led to multiple approaches for measuring and mitigating marine pollution, in order to achieve sustainable marine water quality. Satellite remote sensing, covering large and remote areas, is considered useful for detecting and monitoring marine pollution. Recent developments in sensor technologies have transformed remote sensing into an effective means of monitoring marine areas. Different remote sensing platforms and sensors have their own capabilities for mapping and monitoring water pollution of different types, characteristics, and concentrations. This chapter will discuss and elaborate the merits and limitations of these remote sensing techniques for mapping oil pollutants, suspended solid concentrations, algal blooms, and floating plastic waste in marine waters
There is scientific evidence of accelerated sea level rise and saline intrusion. Some impacts, such as stratification and estuarine circulation are subtle; others are dramatic including shifts in salt-sensitive habitats and limited water availability of suitable quality for industrial and municipal uses. These results have become a remarkable reality resulting in a set of integrated surface water organisation issues. Tremendous population increases overwhelming many coastal areas have expanded the problem. These challenges have been studied from many perspectives using various objectives and methodologies, and then arriving at different findings. However, all research assured that significant rises in sea level have influenced estuaries and tidally affected rivers, and these observations are expected to become rapidly worse in the future. This study introduces categorises, critically investigates, and synthesises the most related studies regarding accelerated sea level rise and challenges of the development associated with the resources of surface water in estuaries and tidally-affected rivers. This critical review reveals that there is a need for research that focuses on the development of sustainable surface water resources.
Spectra, salinity, total suspended solids and colored dissolved organic matter are sampled at 44 locations in the Pearl River estuary on December 18, 19 and 21, 2006. The samples are analyzed. Based on the experimental results, the relationship between the absorption coefficient of chromophoric dissolved organic matter (CDOM; g 400) and the remote sensing reflectance is obtained. In the Modaomen waterway, the result shows that there is a strong positive linear relationship between the in-situ reflectance ratio (R 704/R 513) and g 400 (R 2=0.7, P<0.001); and in the Humen waterway, a negative linear relationship between the in-situ reflectance ratio (R 703/R 488) and g 400 (R 2=0.58, P<0.001) is found. Additionally, the absorption coefficient of CDOM and the salinity in the two waterways are studied, and the two parameters are highly correlated (R 2>0.67). Finally, using the result of this study, a novel method is developed to monitor the surface salinity distribution in estuarine waters. The new method is validated using the simulated Medium Resolution Imaging Spectrometer Instrument (MERIS) data with satisfactory results. The study demonstrates that the salinity variation in the Pearl River estuary (E RMS<0.308%) can be monitored by remote sensing techniques (e. g., MERIS).
This research explored the potential of the use of the CCD image of the HJ satellite to derive Suspended Sediment Concentrations (SSC) of dynamic water bodies at Hangzhou Bay, which is a typical turbid water body in China. Through the analysis on the correlation between Remote Sensing Reflectance (R n) and SSC, two apparent reflectance peaks at approximately 690 and 830 nm have been found in the third and fourth bands, respectively. The result also shows that a good correlation exists between Rn and SSC when the wavelength is more than 700 nm. Based on the measured correlation between SSC and Rn, the retrieval model is established using the ratio of band4 and band3 as remote sensing factor, and the model determination coefficient of 0.90 is reached. Through the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived Aerosol Optical Depth (AOD) data, which are calculated from the Near Infrared-Short Wave Infrared (NIR-SWIR) atmospheric correction, the atmospheric correction of HJ CCD imagery is realized. The correction-relative errors of the third and fourth bands are 5.54% and 6.97%, respectively. The result demonstrates that the relative error of SSC derived from HJ CCD imagery is 7.12%, and SSC at Hangzhou Bay, which also has significant internal diversity, is much higher than that in the entrance of the Yangtze River. This research demonstrated that HJ CCD imagery can be used to evaluate SSC at Hangzhou Bay, if the appropriate atmospheric correction method and retrieval algorithm are used.
Introduction: The Hyperspatial Perspective Hyperspatial image acquisition Issues, potential problems and plausible solutions From data acquisition to fluvial form and process understanding Conclusion Acknowledgements References
Appropriate integration of remote sensing technologies into ecosystem services concepts and practices leads to potential practical benefits for the protection of biodiversity and the promotion of sustainable use of Earth's natural assets. The last decade has seen the rapid development of research efforts on the topic of ecosystem services, which has led to a significant increase in the number of scientific publications. This systematic review aims to identify, evaluate and synthesise the evidence provided in published peer reviewed studies framing their work in the context of spatially explicit remote sensing assessment and valuation of ecosystem services. Initially, a search through indexed scientific databases found 5920 papers making direct and/or indirect reference to the topic of “ecosystem services” between the years of 1960 and 2013. Among these papers, 211 make direct reference to the use of remote sensing. During the search we aimed at selecting papers that were peer-reviewed publications available through indexed bibliographic databases. For this reason, our literature search did not include books, grey literature, extended abstracts and presentations. We quantitatively present the growth of remote sensing applications in ecosystem services’ research, reviewing the literature to produce a summary of the state of available and feasible remote sensing variables used in the assessment and valuation of ecosystem services. The results provide valuable information on how remotely sensed Earth observation data are used currently to produce spatially-explicit assessments and valuation of ecosystem services. Using examples from the literature we produce a concise summary of what has been done, what can be done and what can be improved upon in the future to integrate remote sensing into ecosystem services research. The reason for doing so is to motivate discussion about methodological challenges, solutions and to encourage an uptake of remote sensing technology and data where it has potential practical applications.
Chlorophyll-a (chl-a) is considered as a primary indicator for water quality and foods for oyster growth in Apalachicola estuarine ecosystem. Assessment of chl-a concentration variation in response to river inflow is important for estuarine environmental research and management. In this study, remote sensing analysis has been conducted to evaluate the effects of river inflow on chlorophyll concentrations in Apalachicola Bay of Florida in the northeast Gulf of Mexico. A remote sensing model for chl-a was improved and applied to map spatial distributions of chl-a by using Moderate Resolution Imaging Spectroradiometer (MODIS) 250-m resolution imageries in high-flow and low-flow seasons in 2001 and 2008. Chl-a values approximately ranged from the minimum 6 μg/l to the maximum 29 μg/l in the study period. Maximum chl-a concentration in high-flow season was almost twice above that in low-flow season. The averaged mean and minimum chl-a level in the high-flow season were approximately 42 and 28 % higher than those in low-flow season, respectively. The remote sensing mapping of chl-a was able to show spatial variations of chl-a in the entire bay under different flow conditions, which indicated its advantage over the traditional field data sampling for monitoring water quality over a large area of estuary. The MODIS 250-m remote sensing regression model presented from this study can be used to support monitoring and assessment of the spatial chl-a distribution in the bay for environmental research and management in Apalachicola Bay.
The water from Tai Lake was analyzed by spectrum measurement and synchronous sampling with field portable spectroradiometer. The characteristic wave peaks of cyanobacteria and suspended particle were obtained from the spectra, and the corresponding relations between the heights of wave peaks and the concentrations of chlorophyll a and suspended particle were built. As a result, a quantitative retrieval algorithm is deduced, and the algorithm is applied in the image acquired by OMIS imaging spectroradiometer.
This study was conducted to establish correlations between reflectance spectra and water quality indexes of the Huangpujiang River of Shanghai, sampled in August and November of 2002.31 typical stations were selected to measure the spectral reflectance and 9 water quality parameters were analyzed for every measured stations,including Total Phosphorous（TP）,Total Nitrogen（TN）,Chemical Demand Oxygen with potassium permanganate(CODMn) and with chromate (CODCr),Dissolved Oxygen（DO）,Biological Demand Oxygen（BOD5）,Suspended Sediments and Turbidity.With significant correlation between the nine water quality indexes,TN and suspended sediment concentration were selected,then the paper mainly analyzed the correlations between the two water quality indexes and the normalized reflectance,its logarithm,derivative spectrum,and the ratio of spectral reflectance at different bands.The characterized bands were analyzed for the two water quality parameters with single band normalized spectral reflectance and the first derivative reflectance,and the linear models were built between the water quality parameters and the spectral reflectance ratios of different band,all these models had the good correlation coefficient of more than 0.75 between the two parameters and the spectra reflectance.
Estuary areas are characterized optically by high concentrations of water constituents. A comparison of river total suspended solid (TSS) concentration determined using different bandwidth sensors, ALI and Hyperion, which is based on inverse modelling of in situ sampling and water surface spectra, enables us to estimate TSS at a free selection between the ALI and Hyperion sensors. We employed a semi-empirical method in a comparative analysis of river TSS concentration estimated from ALI and Hyperion data in the Pearl River estuary, as a case study demonstrating the usefulness and the differences in ALI and Hyperion data for suspended solids concentration estimation. The validation snowed there is a good correlation between ALI and Hyperion inverse TSS and the estimation of the concentration of TSS was accurate. However, the ALI-based inversion result underestimates TSS, with larger error values from real values of TSS within the shorter band range.
The spectral absorption coefficient is one of the inherent optical properties that influence the reflectance of aquatic systems. Therefore, knowledge of total absorption and its component parts is required to improve our understanding of variability in spectral reflectance estimated with ocean color sensors. Protocols for estimating the volume absorption coefficients for particles, phytoplankton, photosynthetic pigments, de- pigmented particles and soluble material are described. Methods are based on prior literature and results from NASA-sponsored workshops on methodological protocols. Issues, assumptions, and alternative methods are reviewed and recommendations for future research are made. Workshop participants are listed in Table 1.
The distributions of colored dissolved organic matter (CDOM) and of dissolved organic carbon (DOC) were studied in the Pearl River Estuary from 18 to 26 July 1999 (during the wet season). The highest level of CDOM was found in the fresh water, and lowest in the sea water, indicating the river water is a main source of CDOM in this estuary and may has impact on the optical properties of the South China Sea. However, the CDOM concentration is relatively low compared to the reports from other estuaries in the world. CDOM also did not show a conservative mixing behavior in the Pearl River Estuary. This non-conservative behavior may not be due to removal processes (such as flocculation and photodegradation), but is probably the result of different water mass sources having distinct CDOM composition and optical properties. DOC concentration, contrary to CDOM, varied little with the salinity gradient, leading to a different distribution between CDOM and DOC in the Pearl River Estuary. The absence of a co-variation between CODM with DOC suggests that the contribution of CDOM to DOC is variable and it is probably not feasible to estimate DOC by the remote sensing of CDOM in the Pearl River Estuary.
Three methods for converting Airborne Visible / Infrared Imaging Spectrometer (AVIRIS) radiance data to apparent surface reflectance were compared using data collected over the Lunar Crater Volcanic Field in Nevada and the Pavant Butte tuff cone in Utah. The methods examined were the empirical line method, radiative transfer modeling (using LOWTRAN 7), and spectral mixture analysis using reference endmembers. Of the three, the empirical line and spectral mixture methods both provided good results. The approach utilizing LOWTRAN 7 accentuates noise inherent in AVIRIS data and requires a very accurate estimate of atmospheric water.
Various empirical techniques have been developed to identify turbid marine waters within satellite ocean color imageries. The present technique, which essentially rests on the enhancement of reflectance in the green part of the spectrum when sediments are present, accounts for the improved knowledge regarding the relationship between the chlorophyll concentration and the scattering coefficient in oceanic case-1 waters. It also accounts for the bidirectional character of the light field emerging from a water body and thus for the sensitivity of the water-leaving radiance to the observational conditions (viewing angle and sun angle). Therefore, the thresholds, above which the turbid waters can be detected, are not constant. They depend on the chlorophyll concentration and on geometry (on the zenith-sun angle). The practical way of implementing such a discriminating tool is explained. Examples of the application of this technique are provided for level-2 and level-3 satellite data (SeaWiFS and MERIS).
The utility of satellite imagery for water quality studies in New York Harbor is investigated. Ground data from a routine sampling program (New York Harbor Water Quality Survey) are compared to imagery from the Landsat Thematic Mapper (TM) and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. New York Harbor is a challenging environment for remote sensing because of the complex hydrography and strong tidal influence. Using a time-averaged spatial analysis it is shown that turbidity as determined from Secchi depth correlates with Landsat TM red reflectance in regions affected by the Hudson River sediments (N = 21, R2 = 0.85). Based on this correlation the estuarine turbidity maximum of the Hudson River is mapped. Landsat TM red reflectance is also used to identify and map plumes of increased turbidity caused by rainfall runoff and/or spring tide resuspension in Newark Bay. Chlorophyll a concentration correlates with the ratio of Landsat TM green to red reflectance in the eutrophic East River and Long Island Sound (N = 16, R2 = 0.78). Terra MODIS estimates of chlorophyll a show no correlation with ground observations, are biased towards low values and are therefore not directly useable for New York Harbor.
Variations of sediment type (grain size and refractive index) and changing illumination conditions affect the reflectance signal of coastal waters and limit the accuracy of sediment-concentration estimations from remote-sensing measurements. These effects are analyzed from numerous in situ remote-sensing measurements carried out in the Gironde and Loire Estuaries and then reduced and partly eliminated when reflectance ratios between the near infrared and the visible are considered. These ratios showed high correlation with the sediment concentration. On the basis of the obtained relationships, performing correspondence functions were established that allow an accurate estimation of suspended sediments in the estuaries from Système Probatoire d'Observation de la Terre, Landsat, and Sea-Viewing Wide Field-of-View Sensor data, independently of the date of acquisition.
When resources are scant, C. elegans larvae arrest as long-lived dauers under the control of insulin/IGF- and TGFbeta-related signaling pathways. However, critical questions remain regarding the regulation of this developmental event. How do three dozen insulin-like proteins regulate one tyrosine kinase receptor to control complex events in dauer, metabolism and aging? How are signals from the TGFbeta and insulin/IGF pathways integrated? What gene expression programs do these pathways regulate, and how do they control complex downstream events?
We have identified genes that show different levels of expression in a comparison of wild-type L2 or L3 larvae (non-dauer) to TGFbeta mutants at similar developmental stages undergoing dauer formation. Many insulin/IGF pathway and other known dauer regulatory genes have changes in expression that suggest strong positive feedback by the TGFbeta pathway. In addition, many insulin-like ligand and novel genes with similarity to the extracellular domain of insulin/IGF receptors have altered expression. We have identified a large group of regulated genes with putative binding sites for the FOXO transcription factor, DAF-16. Genes with DAF-16 sites upstream of the transcription start site tend to be upregulated, whereas genes with DAF-16 sites downstream of the coding region tend to be downregulated. Finally, we also see strong regulation of many novel hedgehog- and patched-related genes, hormone biosynthetic genes, cell cycle genes, and other regulatory genes.
The feedback regulation of insulin/IGF pathway and other dauer genes that we observe would be predicted to amplify signals from the TGFbeta pathway; this amplification may serve to ensure a decisive choice between "dauer" and "non-dauer", even if environmental cues are ambiguous. Up and down regulation of insulin-like ligands and novel genes with similarity to the extracellular domain of insulin/IGF receptors suggests opposing roles for several members of these large gene families. Unlike in adults, most genes with putative DAF-16 binding sites are upregulated during dauer entry, suggesting that DAF-16 has different activity in dauer versus adult metabolism and aging. However, our observation that the position of putative DAF-16 binding sites is correlated with the direction of regulation suggests a novel method of achieving gene-specific regulation from a single pathway. We see evidence of TGFbeta-mediated regulation of several other classes of regulatory genes, and we discuss possible functions of these genes in dauer formation.
Spectral measurements of remote-sensing reflectance (Rrs) and absorption coefficients carried out in three European estuaries (Gironde and Loire in France, Tamar in the UK) are presented and analyzed. Typical Rrs and absorption spectra are compared with typical values measured in coastal waters. The respective contributions of the water constituents, i.e., suspended sediments, colored dissolved organic matter, and phytoplankton (characterized by chlorophyll-a), are determined. The Rrs spectra are then reproduced with an optical model from the measured absorption coefficients and fitted backscattering coefficients. From Rrs ratios, empirical quantification relationships are established, reproduced, and explained from theoretical calculations. These quantification relationships were established from numerous field measurements and a reflectance model integrating the mean values of the water constituents' inherent optical properties. The model's sensitivity to the biogeochemical constituents and to their nature and composition is assessed.
The Yellow Sea and East China Sea are typical Case II waters with high sediment load and complicated inherent optical properties. In this paper, several neural network (NN) models are established to retrieve the three major components (chlorophyll, total suspended matter and gelbstoff) concentrations from remote sensing reflectance (Rrs). The NN results are validated with in situ data and also compared with that of the empirical algorithms. The data set was obtained from the Joint Ocean Color Experiments in Yellow Sea and East China Sea in spring 2003. Two types of NN models are proposed, one is to retrieve the three-component concentrations simultaneously in one model (NN3) and the other type of model is to derive each component's concentrations with an individual model (NN1). The accuracy of the NN3 model is inferior to the statistical algorithms, and the averaged relative errors are 44.4% for chlorophyll, 40.5% for total suspended matter (TSM) and 48.8% for gelbstoff, respectively. The accuracy of the NNl models are better than the statistical ones, and the averaged relative errors are 32.5% for chlorophyll and 29.4% for TSM, respectively. Different input combinations of bands or band ratios to NN models reveal the signal sensitivity of different ocean color bands in retrieving the three components. Sensitivity analysis shows that the NNl models of TSM and gelbstoff are not sensitive to ±5% error of input signals, the errors increased are comparable to the statistical algorithms. The NNl chlorophyll model is somewhat sensitive to one case of ±5% input noise. The NN models presented here are the preliminary and usable results for the area.
In this study, field measurements of remote sensing reflectance (Rrs) and laboratory measurements of the absorption coefficient (a) were carried out for two European estuaries: Tamar (UK) and Gironde (France). Additional Rrs measurements were carried out in a third estuarine environment: Loire (France). Typical a and Rrs spectra, and their associated spatio-temporal variations, are presented together with their respective contributions to the biogeochemical constituents: coloured dissolved organic matter, suspended sediments and phytoplankton. Mean values for the specific absorption coefficients (per unit concentration) were obtained. The Rrs signal was reproduced using a bio-optical model, integrating the measured a coefficients and predicted back-scattering (bb) coefficients. Its sensitivity to the biogeochemical constituents and their nature/composition was assessed. The detection limits of the different constituents were estimated based on their respective concentrations, of particular interest was the detection and quantification of the Chla threshold in highly turbid estuarine waters. The Rrs signal was then related to the biogeochemical concentrations with empirical relationships established, reproduced and explained from theoretical calculations. MEASUREMENTS AND ANALYSES Sampling Dates And Locations
In the context of object-oriented video coding, the encoding of segmentation maps defined by contour networks is particularly
critical. In this paper, we present a lossy contour network encoding algorithm where both the rate distortion contour encoding
based on maximum operator and the prediction error for the current frame based on quadratic motion model are combined into
a optimal polygon contour network compression scheme. The bit rate for the contour network can be further reduced by about
20% in comparison with that in the optimal polygonal boundary encoding scheme using maximum operator in the rate distortion
sense.
The feasibility of utilising the multiband ground truth radiometer (MGTR) for monitoring the pollution of the river Ganga by tanneries at Kanpur, India is explored. Parameters targeted in the study were Secchi depth (a measure of turbidity), turbidity, tannin concentration and chemical oxygen demand (COD). MGTR offers reflectance in 11 bands within the spectral range of 0.45 to 0.90 μm. The reflectance data has been utilised to develop empirical relationships with Secchi depth, turbidity and tannin concentration. The spectral reflectance data does not directly indicate the measure of the COD. However, an empirical relationship between tannin concentration and COD has been established which allows an indirect measurement of the COD. The conventional environmental engineering laboratory approach for determination of the above parameters is time consuming, expensive and slow. This results in serious constraints in monitoring pollution parameters at frequent intervals for a large number of sampling points. The outcome of the study shows the viability of MGTR as a means of quick, repetitive and handy remote sensing for monitoring pollution caused by tanneries in narrow surface streams.
An experimental method for determining water composition from “ocean colour” satellite data, in visible and near-infrared (NIR) wavelengths, is applied to highly turbid waters. Numerous spectroradiometric measurements are carried out in the Gironde estuary, for suspended particulate matter (SPM) concentrations ranging between 35 and more than 2000 mg l−1. Empirical relationships are established between remote-sensing reflectance (Rrs) in SPOT-HRV bands and SPM concentration through these numerous in situ measurements. We observed that remote-sensing reflectance increases with SPM concentration and that the SPOT bands saturate at the highest turbidities. The best correlations are obtained for the NIR band XS3 (790–890 nm) and for the reflectance ratios: Rrs(XS3)/Rrs(XS1) and Rrs(XS3)/Rrs(XS2). The XS1 and XS2 visible bands are only used to determine SPM concentrations in the lower part of the estuary (where the SPM concentrations are lower). As a result, SPM concentrations within the surface waters in the estuary are estimated up to 2000 mg l−1 with an accuracy better than ±35%. The algorithm is finally applied to a SPOT scene. Satellite data are corrected for atmospheric effects using a radiative transfer code and in situ reflectance measurements; as a result, the horizontal distribution of SPM is retrieved. Moreover, the high spatial resolution HRV-SPOT sensor shows detailed sedimentary flows, especially in the visible XS1 and XS2 spectral bands.
Optical Properties and Remote Sensing of Inland and Coastal Waters discusses the methodology and the theoretical basis of remote sensing of water. It presents physical concepts of aquatic optics relevant to remote sensing techniques and outlines the problems of remote measurements of the concentrations of organic and inorganic matter in water. It also details the mathematical formulation of the processes governing water-radiation interactions and discusses the development of bio-optical models to incorporate optically complex bodies of water into remote sensing projects. Optical Properties and Remote Sensing of Inland and Coastal Waters derives and evaluates the interrelationships among inherent optical properties of natural water, water color, water quality, primary production, volume reflectance spectra, and remote sensing. This timely and comprehensive text/reference addresses the increasing tendency toward multinational and multidisciplinary climate studies and programs.
During the last two years, a series of beam parameters measurement,
subsystem checkout, installation of various sensors, control program
modification and hardware upgrade made the top-up injection possible in
practical routine operation. Top-up injection is an operation mode in
which the beam current in the storage ring is maintained above certain
level by frequent injections. The routine current stability is in the
range of 10-3 for long period of operation. The Top-up injection
provides advantages in operation such as lower emittance, higher
current, smaller coupling, smaller ID gaps, exotic bunch filling
patterns, and higher bunch charge. It also provides constant thermal
loading on all components in the storage ring and the optics components
of beamlines, as well as constant signal to the beam position monitor.
Discussions on the results of some measurements of booster and storage
ring, the requirement of hardware upgrade and the summary of routine
Top-up operation will be presented in this paper.
The suitability of the AISA airborne imaging spectrometer for monitoring lake water quality was tested in four surveys carried out in southern Finland in 1996-1998. Altogether, 11 lakes were surveyed and the total number of stations with concurrent remote sensing and limnological measurements was 127. The ranges of the water quality variables were: the sum of chlorophyll a and phaeophytin a 1-100 microg l(-1), turbidity 0.4-26 FNU, total suspended solids 0.7-32 mg l(-1), absorption coefficient of aquatic humus at 400 nm 1.2-14 m(-1) and secchi disc transparency 0.4-7 m. For the retrieval analyses, 24 AISA channels in the 450-786 nm range with a channel width of 6-14 nm were used. The agreement between estimated and observed water quality variables was generally good and R2 for the best algorithms was in the range of 0.72-0.90 over the whole dataset. The channels used for May were, in most cases, the same as those for August, but the empirical parameters of the algorithms were different. After seasonal grouping, R2 varied from 0.84 to 0.95. The use of apparent reflectance instead of radiance improved the estimation of water quality in the case of total suspended solids and turbidity. In the most humic lake, the empirical algorithms tested were suitable only for the interpretation of total suspended solids and turbidity.
Spectral absorption coefficients of the total particulate, a
p(λ), nonalgal particulate, a
d(λ), and phytoplankton pigment, a
ph(λ), in the Pearl River estuary and its vicinity waters were determined using the quantitative filter technique. The particulate
absorption a
p(443) ranged from 0.04 to 1.82 m−1, with the corresponding a
ph(443) ranging from 0.016 to 0.484 m−1. Two typical spectral patterns are found for the total particulate absorption. For the first typical spectral pattern, the
total particulate absorption spectra are similar to that of nonalgal particulate, with values of absorption coefficient decreasing
with wavelength. In contrast, for the second spectral pattern the spectral absorptions by total particulate are very similar
to that of phytoplankton pigment. The spectral dependency of absorption by nonalgal particulate follows an exponential increase
toward short wavelengths, with an average slope of 0.012 ± 0.002 nm−1. The nonalgal absorption and the fraction of the nonalgal particulate absorption to the total particulate absorption exhibit
a distinct trend of decreasing with salinity of the surface water. Phytoplankton pigment absorption exhibits a clear trend
of increasing nonlinearly with chlorophyll a concentration. The relationships between the phytoplankton pigment absorption
and chlorophyll a concentration can be described by power law, with the determination coefficient r
2 of 0.82. But only weak relationships between a
p(λ) and chlorophyll a concentration are observed, with the determination coefficient r2 of 0.42. The relatively large scatter around a
p(443) versus chl-a relationship would be attributed to the effects of loading of the nonalgal particulate absorption. Our
analysis indicated that such relationships similar to that for Case I waters can be applicable to optically complex Case II
waters if the effects caused by nonalgal are corrected. The chlorophyll-specific absorption coefficients of phytoplankton
pigment are not constant, it increases with decreasing chlorophyll a level. To improve the accuracy of bio-optical algorithms
for remote sensing in coastal waters, further investigations on the variations of specific absorption of chlorophyll pigment
must be made.
An experimental method for determining water composition from “ocean colour” satellite data, in visible and near-infrared (NIR) wavelengths, is applied to highly turbid waters. Numerous spectroradiometric measurements are carried out in the Gironde estuary, for suspended particulate matter (SPM) concentrations ranging between 35 and more than 2000 mg l−1. Empirical relationships are established between remote-sensing reflectance (Rrs) in SPOT-HRV bands and SPM concentration through these numerous in situ measurements. We observed that remote-sensing reflectance increases with SPM concentration and that the SPOT bands saturate at the highest turbidities. The best correlations are obtained for the NIR band XS3 (790–890 nm) and for the reflectance ratios: Rrs(XS3)/Rrs(XS1) and Rrs(XS3)/Rrs(XS2). The XS1 and XS2 visible bands are only used to determine SPM concentrations in the lower part of the estuary (where the SPM concentrations are lower). As a result, SPM concentrations within the surface waters in the estuary are estimated up to 2000 mg l−1 with an accuracy better than ±35%. The algorithm is finally applied to a SPOT scene. Satellite data are corrected for atmospheric effects using a radiative transfer code and in situ reflectance measurements; as a result, the horizontal distribution of SPM is retrieved. Moreover, the high spatial resolution HRV-SPOT sensor shows detailed sedimentary flows, especially in the visible XS1 and XS2 spectral bands.
The Pearl River is a complex river network under the influence of heavy urbanization and industrialization. The Pearl River Estuary receives freshwater from eight major sources, each containing various pollutants. The spectral absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) in the Pearl River Estuary were studied during November 2002, a low flow (dry) season. Over a salinity range of 33–0, CDOM absorption coefficients at 355 nm (a(355)) ranged from 0.24 to 1.93 m− 1, lower than several other American and European estuaries. In contrast to the wet season, conservative mixing was evidenced by a linear, inverse relationship between a(355) and salinity. CDOM, primarily of terrestrial origin, contained more anthropogenic organic matter than natural plant decay matter: tryptophan-like fluorophore T had the strongest signal among all fluorophores for the entire study region. The absorption spectral slope (S), determined between 300 and 500 nm, ranged between 0.0138 and 0.0184 nm− 1 and did not show distinguishable patterns except in the transition zone between the estuary and the South China Sea. The relative composition of fluorophores was found to vary among different sources. This result demonstrated the potential for using fluorophores to characterize the composition of CDOM and trace pollutants to their various freshwater sources.
This study investigates the use of single-band reflectance at visible wavelengths for the derivation of suspended sediment concentrations in the Irish Sea. A reasonably strong relationship was observed between irradiance reflectance at 665 nm (R665) and mineral suspended sediment (MSS) concentrations. Variability in the Reflectance–MSS relationship was found to be the consequence of changes in the mass-specific scattering coefficient (bMSS*) brought about by differences in particle properties such as grain size and composition. A systematic increase in the slope of the Reflectance–MSS relationship was observed with increasing bMSS*. A reflectance model is presented that highlights the dependence of reflectance on bMSS* and suggests that the errors in predicted MSS concentrations can be reduced from 56% to as little as 12% with prior knowledge of the scattering properties of the sediments under study. This paper highlights the need for a complete understanding of the scattering properties of particles in order to accurately estimate MSS concentrations from reflectance measurements. It is suggested that in order to obtain quantitative estimates of MSS in moderately turbid waters from space, it may be necessary to pre-determine scattering efficiencies, bMSS*, for the area of interest.
We developed an approach to map turbidity in estuaries using a time series (May 2003 to April 2006) of 250-m resolution images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite, using Tampa Bay as a case study. Cross-calibration of the MODIS 250-m data (originally designed for land use) with the well-calibrated MODIS 1-km ocean data showed that the pre-launch radiometric calibration of the 250-m bands was adequate. A simple single scattering atmospheric correction provided reliable retrievals of remote sensing reflectance at 645 nm (0.002 < Rrs(645) < 0.015 sr− 1, median bias = − 7%, slope = 0.95, intercept = 0.00, r2 = 0.97, n = 15). A more rigorous approach, using a multiple scattering atmospheric correction of the cross-calibrated at-sensor radiances, retrieved similar Rrs(645). Rrs(645) estimates, after stringent data quality control, showed a close correlation with in situ turbidity (turbidity = 1203.9 × Rrs(645)1.087, 0.9 < turbidity < 8.0 NTU, r2 = 0.73, n = 43). MODIS turbidity imagery derived using the developed approach showed that turbidity in Hillsborough Bay (HB) was consistently higher than that in other sub-regions except in August and September, when higher concentrations of colored dissolved organic matter seem to have caused underestimates of turbidity. In comparison, turbidity in Middle Tampa Bay (MTB) was generally lowest among the Bay throughout the year. Both Old Tampa Bay (OTB) and Low Tampa Bay (LTB) showed marked seasonal variations with higher turbidity in LTB during the dry season and in OTB during the wet season, respectively. This seasonality is linked to wind-driven bottom resuspension events in lower portion of the Bay and river inputs of sediments in the upper portion of the Bay. The Bay also experiences significant interannual variation in turbidity, which was attributed primarily to changes in wind forcing. Compared with the once-per-month, non-synoptic in situ surveys, synoptic and frequent sampling facilitated by satellite remote sensing provides improved assessments of turbidity patterns and thus a valuable tool for operational monitoring of water quality of estuarine and coastal waters such as in Tampa Bay.
For the managers of a region as large as the Great Barrier Reef, it is a challenge to develop a cost effective monitoring program, with appropriate temporal and spatial resolution to detect changes in water quality. The current study compares water quality data (phytoplankton abundance and water clarity) from remote sensing with field sampling (continuous underway profiles of water quality and fixed site sampling) at different spatial scales in the Great Barrier Reef north of Mackay (20 degrees S). Five transects (20-30 km long) were conducted from clean oceanic water to the turbid waters adjacent to the mainland. The different data sources demonstrated high correlations when compared on a similar spatial scale (18 fixed sites). However, each data source also contributed unique information that could not be obtained by the other techniques. A combination of remote sensing, underway sampling and fixed stations will deliver the best spatial and temporal monitoring of water quality in the Great Barrier Reef.
Post-evaluation of influence of Modaomen estuarine regulation project on water environment
- H P Jiang
- D K Wang
- D G Wang
Jiang, H.P., Wang, D.K., Wang, D.G., 2002. Post-evaluation of influence of Modaomen
estuarine regulation project on water environment. Journal of Hohai University
(Natural Sciences) 30, 67-69 (in Chinese with English Abstract).
The spectral features analysis and quantitative remote sensing advances of inland water quality parameter
- Li
Li, S.J., Wang, X.J., 2002. The spectral features analysis and quantitative remote
sensing advances of inland water quality parameter. Geography and Territorial
Research 18, 26-30 (in Chinese with English Abstract).
Study on the cause of formatting high turbidity water in Macau Estuary of Pearl River and its solving way
- L Li
- J Xiao
- Y S Min
Li, L., Xiao, J., Min, Y.S., 1999. Study on the cause of formatting high turbidity water in
Macau Estuary of Pearl River and its solving way. Journal of South China University
of Technology (Natural Science) 27, 93-97 (in Chinese with English Abstract).
Surface water quality monitoring using remote sensing
- Y Z Zhang
- Y P Nie
- Q Z Lin
- L H Jing
- B Zhang
Zhang, Y.Z., Nie, Y.P., Lin, Q.Z., Jing, L.H., Zhang, B., 2000. Surface water quality
monitoring using remote sensing. Remote Sensing Technology and Application
15, 214-219 (in Chinese with English Abstract).
Study on the formation and countermeasure of water with high turbidity in Macao estuary of the Pearl River
- Li
Li, L., Xiao, J., 2000. Study on the formation and countermeasure of water with high
turbidity in Macao estuary of the Pearl River. Environmental Protection In
Transportation 21, 13-15 (in Chinese).
Research on the integrated technology of purification in Yellow River high-turbid water treatment
- J X Nie
- X Fang
- W S Han
- X M Gao
Nie, J.X., Fang, X., Han, W.S., Gao, X.M., 2001. Research on the integrated technology
of purification in Yellow River high-turbid water treatment. Journal of
Northwest Institute of Architecture and Engineering (Natural Science) 18, 165-169 (in Chinese with English Abstract).
Spectral absorption coefficients of particulate matter and chromophoric dissolved organic matter in Meiliang Bay of Lake Taihu
- Y L Zhang
- B Q Qin
- L Y Yang
Zhang, Y.L., Qin, B.Q., Yang, L.Y., 2006. Spectral absorption coefficients of particulate
matter and chromophoric dissolved organic matter in Meiliang Bay of Lake
Taihu. Acta Ecologica Sinica 26, 3969-3979.
The variable relations between the turbidity and suspended matter in the sea water during the dredging process of the channel in Dayao Bay
- G K He
- M H Shao
- B S Gao
- R Y Liu
He, G.K., Shao, M.H., Gao, B.S., Liu, R.Y., 1994. The variable relations between the
turbidity and suspended matter in the sea water during the dredging process of
the channel in Dayao Bay. Marine Environmental Science 13, 76-82 (in Chinese
with English Abstract).
Post-evaluation of influence of Modaomen estuarine regulation project on water environment Retrieval of water quality from airborne imaging spec-trometry of various lake types in different seasons
- H P Jiang
- D K Wang
- D G K Wang
- T Kutser
- T Hannonen
- S Koponen
- J Pulliainen
- Vepsä
- J Inen
- T Pyhä Lahti
Jiang, H.P., Wang, D.K., Wang, D.G., 2002. Post-evaluation of influence of Modaomen estuarine regulation project on water environment. Journal of Hohai University Kallio, K., Kutser, T., Hannonen, T., Koponen, S., Pulliainen, J., Vepsä lä inen, J., Pyhä lahti, T., 2001. Retrieval of water quality from airborne imaging spec-trometry of various lake types in different seasons. The Science of The Total Environment 268, 59–77.
Study on the cause of formatting high turbidity water in Macau Estuary of Pearl River and its solving way
- Li
Research on the integrated technology of purification in Yellow River high-turbid water treatment
- Nie
The variable relations between the turbidity and suspended matter in the sea water during the dredging process of the channel in Dayao Bay
- He
Post-evaluation of influence of Modaomen estuarine regulation project on water environment
- Jiang
Surface water quality monitoring using remote sensing
- Zhang