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The utilization of satellite altimeter data sets from previous and present satellite altimeter missions is imperative to both oceanographic and geodetic applications. The important parameter that can be derived from satellite altimeter is sea level anomaly, while it is also fundamental for sea level monitoring, geoid determination and current circu...
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... satellite altimeter program was originally started at the 1969 Williamstown Conference. An altimeter was actually used to scan the Moon by Apollo 14. The first dedicated altimeter mission was GEOS-3 (April 1975 to December 1979), with a measurement precision of 25 cm in the second (s) averages. Technological improvements increased this measurement precision for 1 s averages to about 5 cm for the SEASAT altimeter, which was operated from July to October 1978. Further improvements have resulted in better than 5 cm precision on the presently operational (since March 1985) GEOSAT altimeter [1]. Satellite altimeter measurements have now been continuously available since 1991, through the ERS1, TOPEX/Poseidon, ERS2, GEOSAT Follow-on, JASON1, JASON2, ENVISAT, CRYOSAT2 and SARAL missions. Measurements from these instruments have revolutionized our knowledge of the ocean, through studies in sea level, ocean circulation and climate variability. More details on altimetry and its applications can be found in Fu and Cazenave [2001]. Although satellite altimeter records are still quite short compared to the tide gauge data sets (For sea level anomaly determination case), this technique appears quite promising especially for the sea level study because it provides sea level measurement with large coverage. A precision of about 1 mm/year of measurement global change can be obtained [2]. Six satellite altimeter missions were used to derive sea level anomaly in this study; TOPEX, JASON1, JASON2, ERS1, ERS2 and ENVISAT. Details for each characteristic and orbit of satellite missions are described in Table 1. Satellite altimeter data has been distributed through agencies like NOAA, AVISO, EUMETSAT and PO.DAAC. In addition to these agencies, the Delft Institute for Earth-Oriented Space Research (DEOS) and the NOAA Laboratory for Satellite Altimetry has been collaborating in the development of Radar Altimeter Database System (RADS). The RADS is established in a harmonized, validated and cross-calibrated sea level database from all satellite altimeter missions. In RADS, users able to access to the most present range and geophysical corrections and also can produce their own altimetric products based on their particular interest [4]. In the frame of RADS, the DEOS is developing a database that incorporates validated and verified altimetry data products. Besides, the database is also consistent in accuracy, correction, format and reference system parameters. The capability of such a database will attract users with less satellite altimeter expertise like advisory councils, water management authorities and even high schools [5]. This system also fulfills the need of scientists and operational users to have value-added sea level data readily at one’s disposal [6]. Currently, RADS enables users to extract the data from several present and past satellite altimeter missions like GEOSAT, ERS1, ERS2, ENVISAT, TOPEX/Poseidon (T/P), JASON1, JASON2, CRYOSAT2 and SARAL. In Universiti Teknologi Malaysia (UTM), the RADS system has been installed since 2005 in the frame of the SEAMERGES project, an EU funded project (AUNP) that aimed for knowledge, methods and data exchange related to satellite altimetry, InSAR and GPS (www.deos.tudelft.nl/seamerges). Several universities and research group from France and the Netherlands (Europe representative), and Malaysia, Indonesia, and Thailand (South East Asia representative) are participating in this geodetic education and geodetic research project. The main goal of the SEAMERGES project is to accomplish the knowledge transfer, expertise and technology from Europe to South East Asia to locally enable the geodetic research at higher-level and to initiate the implementation of these technologies in the water management and risk assessment applications. It also aims at encouraging the scientific cooperation and collaboration among the different South East Asia countries. The basic principle of satellite altimeter is based on the simple fact that time is a distance. The distance between the satellite and the sea surface is measured from the round-trip travel time of microwave pulses emitted downward by the satellite radar, reflected back from the ocean, and received again on board. Meanwhile, the independent tracking systems are used to compute the satellite’s three -dimensional position relative to a fixed Earth coordinate system. By combining these two measurements yields profiles of sea surface height, or sea level, with respect to the reference ellipsoid [2]. However, the situation is far more complex in practice. Several factors have to take into account such as instrument design, calibration, validation, range corrections (ionosphere, troposphere and sea state bias), geophysical corrections (tides, geoid and inverse barometer), reference systems, precise orbit (satellite height) determination, different satellites with different sampling characteristics, and so on. Figure 1 presents the schematic diagram of satellite radar altimeter system and its principle. By using a similar notation to [1], the corrected range R corrected is related to the observed range R ...
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... Meanwhile, the three-dimensional position of the altimeter in relation to a fixed Earth coordinate system is determined using an independent tracking mechanism. Din et al., [25] stated that merging these two measurements (i.e., altimeter signal measurement and altimeter position) produces sea surface heights' profile or ocean level with reference to the ellipsoid. The emission of short pulse radiation and measuring the time taken of signal travelled to the sea surface and back to the satellite are called altimeter range, , which describes the satellite's height above the ocean surface. ...
Since the first launch of the altimeter mission in 1978, it has been significant for ocean studies in many fields. Today, satellite altimeters enable users to use their products for resource assessment. The inadequacy of in-situ data in the coastal and offshore Malaysian Sea has deprived the tidal range resource assessment. The depletion of natural resources and climate change raised the need for sustainable energy. Vast ocean resources surround Malaysia and have the potential to harness tidal range energy. The altimetry mission can provide extensive ocean data in both spatial and temporal resolution. This research used the multi-mission satellite altimeter to estimate HAT and LAT for the tidal range generation and a tide gauge for validation purposes. A GIS approach is adopted to assess the potential location by mapping the resource and marine conflicts. Validation showed that the estimated HAT and LAT have RMSE values of 25.5 cm and 17.4 cm, respectively. Several locations, including the Pahang, Selangor, and Sarawak coasts, are identified, with a potential resource range of 55.25 to 129.33 kW/m 2. This research presents insight into Malaysia's tidal range energy potential, providing valuable information to stakeholders and the government for clean energy development.
... This tide gauge station is located at 103.18 E, 5.27 N, continuously recording tidal measurement . Meanwhile, according to Trisirisatayawong, (2011) and Din et al., (2014), satellite altimeter passes Cendering tide gauge only thrice per month, and in worst-case scenario, only once. where the SLA derived from altimetric and tidal data shows similar fluctuations. ...
Coastal Inundation is the amount of water levels that reach above normal level due to flooding in coastal areas. This natural phenomenon is due to the rising of local sea level. This study aims to develop a coastal inundation simulation along the coastline of Terengganu. To ensure the success of this study, the rate and magnitude of sea level rise are calculated using Radar Altimetry Database System (RADS) from multi-mission satellite altimetry data. The rate of sea level rise is computed using robust fit regression technique and overlaid with global Digital Elevation Model (DEM) data, known as TanDEM-X. The overlaid data are utilised to simulate the probable areas to be affected by inundation from year 2040 to 2100 using ArcGIS software. The results obtained from the period of 1993 to 2015 show that the average rate of sea level rise along the Terengganu shoreline is 4.84 mm/year with a standard deviation of 0.49 mm/year. By 2100, the estimated average regional sea level rise is projected to increase by 0.412 m. This study could help coastal development planning, defence, and safety monitoring.
... Satellite altimetry data implemented in the computation have been preprocessed based on the optimal range and geophysical corrections for the Malaysian region. Most of the ranges and geophysical corrections implemented in this study are based on user manuals and gradual experiences from prior studies (Scharroo et al. 2012;Din et al. 2014Din et al. , 2019Hamid et al. 2018;Zulkifle et al. 2019). ...
Marine gravity anomalies are crucial parameters and elements for determining coastal and ocean geoid, tectonics and crustal structures, as well as offshore studies. This study aims to derive and develop a marine gravity anomaly model over Malaysian seas from multi-mission altimetry data. Universiti Teknologi Malaysia 2020 Mean Sea Surface Model is computed based on along-track data from nine satellite missions, incorporating TOPEX, Jason-1, Jason-2, ERS-2, Geosat Follow on (GFO), Envisat-1, CryoSat-2, SARAL/AltiKa, and Sentinel-3A. The data exploited are from 1993 to 2019 (27 years). Residual gravity anomaly is computed using Gravity Software, and two-dimensional planar Fast Fourier Transformation method is applied. The evaluation, selection, blunder detection, combination, and re-gridding of the altimetry-derived gravity anomalies and Global Geopotential Model data are demonstrated. Cross-validation procedure is employed for data cleaning and quality control using the Kriging interpolation method. Then, cross-validation procedure is applied to the tapering window width 200, which adopting the GECO model denotes the optimum gravity anomaly with root mean square errors in the range of ± 4.2472 mGal to ± 6.0202 mGal. The findings suggest that the estimated marine gravity anomaly is acceptable to be implemented in the marine geoid determination and bathymetry estimation over Malaysian seas. In addition, the results of this study are valuable for geodetic and geophysical applications in marine areas. Along-track altimetry data are used for mean sea surface derivation.Mean sea surface model is utilised in the estimation of marine gravity anomalies.Global Geopotential Model is crucial in the marine gravity estimation of a region. Along-track altimetry data are used for mean sea surface derivation. Mean sea surface model is utilised in the estimation of marine gravity anomalies. Global Geopotential Model is crucial in the marine gravity estimation of a region.
... Both satellite missions provide the most accurate altimetry data compared to others, mainly due to the precise determination of the orbit. The ground track pattern of these satellites repeats every 10 days, with this temporal sampling providing near-global (within ± 66 ° latitude) maps of sea level changes (Din et al., 2014). ...
... Processing flow of RADS(Din et al., 2014) ...
Upwelling is a vital ocean behaviour, especially for the Fisheries Industry, where upwelling will help to detect fish ground at a particular ocean area. However, the study of upwelling is minimal and not well understood due to some reasons and constraints, such as limited observation. Upwelling lacks a comprehensive in-situ observation system where it relies on limited information collected from the ground-truthing execution such as ships, buoys, and current meter. This study aims to analyse the upwelling pattern in the southern region of the South China Sea by using a multi-mission satellite altimeter. In order to derive the physical oceanography that involves upwelling, such as sea surface height (SSH), Mean Dynamic Topography (MDT), and the Sea Level Anomaly (SLA), the Radar Altimeter Database System is used. Five Satellite Altimeter mission is used in this study, which is JASON-2, JASON-3, CYROSAT2, SARAL, SENTINAL3A from 2013 to 2017. Validation is made using a statistical method showing a good correlation between Altimetry data and Tidal Data at tide gauge, which is 0.84 to 0.97, respectively. Also, monthly altimetry derived Geostrophic Current was assessed by analysing the current pattern where it shows a similarity with a previous study where the current velocity is 0.5ms-1 to 2ms-1. From the result, eddies can be seen in the seasonal and monthly Absolute Geostrophic Ocean Current (AGOC) map, indicating the present presence of upwelling. In conclusion, this study will benefit other researchers in terms of both upwelling and eddy studies.
... Nowadays, satellite altimeters are widely used to improve ocean dynamic studies and to determine absolute sea level from space in order to overcome the problems of existing techniques. In contrast, compared to tide gauge method, satellite altimeters can provide long-term sea level data and monitor sea level changes, particularly in the deep sea region (Feng et al. 2013 andDin et al. 2014). By measuring absolute sea level from the altimetry data, future sea level rate can be projected for the next 100 years. ...
... Therefore, acquiring water height values involves a complicated process. Using the same concept by Fu and Cazenave, (2001) and Din et al. (2014), the corrected range R corrected is related to the observed range R obs . Therefore, the R corrected equation can be expressed as follows: ...
... However, the actual the sea surface height is a superposition of geographical signals. The dynamic sea surface height (h D ) is used to remove the external geographical signals (Fu & Cazenave, 2001;and Din et al. 2014). ...
Global sea level is expected to rise consistently in the future, causing severe damage to the coastal areas and threatening nearby populations. Malaysian coast has numerous low-lying areas, which are at risk of inundation resulting from the increment of sea level, particularly in Kelantan coast. In this study, the potential vulnerability impact of sea level rise has been evaluated using the combination of data from satellite altimeters: global positioning system (GPS) and light detection and ranging (LiDAR). According to our findings, the coastal areas of Kelantan are potentially inundated by sea water in several locations, thus affecting the socio-economy and life of the coastal community. The inundation scenarios for 5, 25, 45, 65 and 85 years of return periods have been successfully simulated using the hydrological model obtained from altimetry data. Subsequently, the inundation scenarios have been overlaid on land elevation datasets to estimate the inundation risks. In order to develop maps for vulnerable areas and populations, vulnerability assessments of inundation risk maps are analysed in ArcGIS environment. The study reveals that the projection of sea level rise is between 32 and 50 cm for the specific area of the Malaysian seas by 2100. The results of the assessment show that the coastal zone of Kelantan is highly vulnerable to the sea level rise. Almost 1km2 of the total land area has been projected to be inundated in the least scenario on local scale. Under the higher sea level scenarios, more than 8.2km2 of the land area are potentially inundated. Up to 46,000 peoples could be affected around the Kelantan coastal and floodplain area, particularly near Kota Bharu. This study highlights the integration of hydrological model to produce inundation risk map that consider the extent of total land area covered by sea level rise in different scenarios.
... The SSH time series were computed by applying the best range and geophysical corrections within the study area. The range and geophysical were adopted from Din et al. (2014) as shown in Table 1. However, ℎ must not be applied into the equation as ocean tide is the signal of interest in this study. ...
... Before performing harmonic analysis, the SSH times series from TOPEX class missions must be derived by applying the best range and geophysical corrections within the study area. The range and geophysical corrections were adopted from Din et al. (2014). Nevertheless, only ocean tide correction was not applied to the SSH time series as the tidal signal is the interest of this study. ...
Satellite altimetry technology has been widely used in exploring Earth’s Ocean activities. Achieving a remarkable accuracy in measuring sea level for ocean tide analysis has led the local researchers to investigate more details on tidal behaviour in the regional area. This study is an attempt to assess the reliability of derived tidal constituents between satellite radar altimetry and in-situ data which is referred to as coastal tide gauges. Three satellite missions denoted as TOPEX class missions namely TOPEX, Jason-1, and Jason-2 were used to derive along-track sea surface height (SSH) time series over 23 years. Besides, four selected coastal tide gauges were used for tidal analysis and validation where the tidal data have at least 19 years of hourly observation. Derivation of tidal constituents from both satellite altimetry and tide gauges were executed by adopting the harmonic analysis method. The comparisons were made by calculating the Root Mean Square Misfit (RMSmisfit) of each tidal constituent between the nearest altimetry point to the tide gauges. After RMSmisfit, Root Sum Square (RSS) values of tidal constituents at each tide gauge were also calculated. The results displayed the RMSmisfit of tidal constituents agreed well with the selected tide gauges which are within 10 cm except for M2 constituents which recorded 10.2 cm. Pelabuhan Kelang tide gauge station showed the highest RSS value followed by Pulau Langkawi which recorded 21.2 cm and 9.8 cm, respectively. In conclusion, overall results can be inferred that the satellite-derived tidal constituents are likely to have good agreement with the selected tide gauge stations. Nevertheless, further analysis should be executed in determining high precision satellite-derived tidal constituents, especially in the complex regional area.
... The Delft Institute for Earth-oriented Space Research (DEOS) previously established the Radar Altimeter Database System or RADS, a database system that integrates authenticated altimetry products, consistently maintained by the international scientific community. This system serves as a processing tool for their altimetry data while allowing the user to define the most appropriate corrections (Naeije et al., 2000; Din et al., 2014). RADS's most significant advantage lies in its ability to combine all SALT missions in terms of crossover adjustments and moving averages (Hamid et al., 2018). ...
Sustaining coastal ecosystems from the impact of rising sea levels is vital since they offer environmental services that are considered critical for humans’ well-being. The Coastal Vulnerability Index (CVI) is favoured in coastal hazard studies, as it provides a predictive approach to coastal changes through its simple numerical basis in classifying coastlines based on their potential to change. The recent widespread use of innovative technologies has contributed to accessible coastal components to investigate coastal hazards and analyse risk assessment. However, most of the studies related to CVI have rarely exploited these forms of technology despite being utilised in various geodetic applications. Hence, a comprehensive review is performed to evaluate the application of these technological advances, particularly on exploiting space geodetic technology to determine and classify coastal information from various analytical approaches. This paper systematised modern approaches utilizing space technology to form CVI to assess the significant processes affecting the vulnerability and evolution of coastal areas. It is envisaged that the exploitation of space technology will facilitate CVI development and promote effective coastal management strategies.
... The improvement of precise orbit determination technique, instrumental and geophysical corrections have provided better accuracy of sea surface height (SSH) measurements since the launch of TOPEX/Poseidon mission [13]. The obtained SSH from satellite altimetry revisits at the similar point for each orbit cycle can be offered as tide gauge measurements at each location globally. ...
Tidal datums are important for calculating spatial coordinates especially the elevation relative to mean sea level and also crucial for defining the state sovereignty boundaries over maritime areas. Normally, sea level was measured by tide gauges along the coastal for tidal datums computation. However, knowledge of tides is still restricted in coastal areas. Furthermore, tidal range at offshore was simply assumed to be similar as coastal due to the difficulties installing offshore tide gauges. The launching of satellite altimeter technologies with precise orbit determination since 1993 had provided significant accuracy of sea surface height (SSH) measurements. The observed SSH from satellite altimetry can be offered as tide gauge measurements at each location globally. This study aims to derive offshore tidal datums using satellite altimetry around Malaysian seas. SSH time series from TOPEX, Jason-1, Jason-2 and Geosat Follow On (GFO) were analysed using harmonic analysis approach to estimate harmonic constants. A minimum of 19 years tidal predictions were then performed using UTide software to determine Lowest Astronomical Tide (LAT) and Highest Astronomical Tide (HAT). These tidal datums were interpolated into regular 0.125° grids and were assessed with ten selected coastal tide gauges. The findings showed the Root Mean Square Error (RMSE) of spline interpolation yielded better accuracy, 25.5 cm (LAT MSL ) and 17.4 cm (HAT MSL ) as compared to the RMSE of Kriging interpolation, 31.8 cm (LAT MSL ) and 33.8 cm (HAT MSL ). In conclusion, deriving offshore tidal datums can serve as input data to unify marine database with coastal areas and also can support many marine applications.
... The measurement of the sea surface height is the concept of satellite altimeter, which can be determined from the time back and forth of the microwave pulse emitted by the satellite altimeter to the sea surface, and the power of the microwave pulse radiation is acknowledged (Chelton et al. 2001;Din et al. 2014;Zulkifle et al. 2019;Hamden et al. 2021). The primary measurement taken by the satellite altimeter is the measurement range, satellite height above the sea surface height as well as the altitude of the satellite with relation to the ellipsoid (orbital height). ...
... The data extraction for SSH can be completed after the required correction has been made. Two corrections are found in the study, namely range and geophysical correction, to obtain the SSH (Din et al. 2014;Abazu et al. 2017). The range correction for obtaining the SSH was automatically applied in this system by using Eq. ...
The conventional bathymetry survey uses a single beam echo sounder (SBES) and multi-beam echo sounder (MBES). However, this technique is challenging to map large ocean areas due to complexity, cost, and time-consuming. This study aims to estimate the multi-mission satellite altimetry bathymetry across the Malaysian Seas. Six satellite altimeter missions with 11 years of data have been utilised to derive mean sea surface height (MSSH). The Gravity-Geologic Method, a conventional terrain inversion method based on gravity data, is employed in this study to estimate bathymetry using a density contrast of 1.67 g cm-3. The gravity-Geologic method utilises gravity effects to be converted into bathymetry by using an inversion process. The density contrast between the bedrock and the seawater influences the predicted bathymetry. Regional gravity was removed from the observed gravity in order to determine the short-wavelength gravity effects by using the control depths from the shipborne measurements. The findings were validated and compared with shipborne bathymetry data from the National Geophysical Data Centre (NGDC) and Global Bathymetry Models. The estimated bathymetry correlation analysis, R, showed the highest values recorded with 0.9942. These findings reveal that the estimated bathymetry using the Gravity-Geologic Method seems to improve the accuracy of the bathymetry by 69% when compared with the ETOPO1 global bathymetry model. Nonetheless, the estimated bathymetry records 38% improvement when compared to the DTU10 global bathymetry model. The final estimated bathymetry model in this study is known as the UTM18 Bathymetry Model.
... This includes rendering and removing invalid data as well as generating the corresponding refined geophysical corrections. Most of the range and geophysical corrections applied for this model are underpinned and guided by user manuals and progressive experiences from previous studies (Scharroo et al., 2013;Din et al., 2014;Yahaya et al., 2016;Hamid et al., 2018;Din et al., 2019;Zulkifle et al., 2019). Supplementary Table S1 differentiates a list of range and geophysical corrections implemented by Yahaya et al. (2016), Zulkifle et al. (2019), and UTM20 MSS. ...
Contemporary Universiti Teknologi Malaysia 2020 Mean Sea Surface (UTM20 MSS) and Mean Dynamic Topography (UTM20 MDT) models around Malaysian seas are introduced in this study. These regional models are computed via scrutinizing along-track sea surface height (SSH) points and specific interpolation methods. A 1.5-min resolution of UTM20 MSS is established by integrating 27 years of along-track multi-mission satellite altimetry covering 1993–2019 and considering the 19-year moving average technique. The Exact Repeat Mission (ERM) collinear analysis, reduction of sea level variability of geodetic mission (GM) data, crossover adjustment, and data gridding are presented as part of the MSS computation. The UTM20 MDT is derived using a pointwise approach from the differences between UTM20 MSS and the local gravimetric geoid. UTM20 MSS and MDT reliability are validated with the latest Technical University of Denmark (DTU) and Collecte Localisation Services (CLS) models along with coastal tide gauges. The findings presented that the UTM20, CLS15, and DTU18 MSS models exhibit good agreement. Besides, UTM20 MDT is also in good agreement with CLS18 and DTU15 MDT models with an accuracy of 5.1 and 5.5 cm, respectively. The results also indicate that UTM20 MDT statistically achieves better accuracy than global models compared to tide gauges. Meanwhile, the UTM20 MSS accuracy is within 7.5 cm. These outcomes prove that UTM20 MSS and MDT models yield significant improvement compared to the previous regional models developed by UTM, denoted as MSS1 and MSS2 in this study.
