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Absolute difference between corrected AVHRR and true (TM) class fractions for various PSA sample sizes.
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We tested the effectiveness of the Purposive Selection Algorithm (PSA, described in the companion first article) to accurately estimate land cover composition over a large area. The knowledge of land cover distribution over large areas is increasingly more important for numerous scientific and policy purposes. Unless a complete detailed map is nece...
Citations
... Do not comment on correct changes. AQ11 The reference ' Cihlar et al. (2000)' is listed in the references list but is not cited in the text. Please either cite the reference or remove it from the references list. ...
Unplanned urban growth, particularly in developing countries has led to changes in land use/land cover (LULC). Numerous Indian cities face problems of unplanned LULC change due to nominal or non-existent planning efforts compounded by rapid urban population growth. The Guwahati Metropolitan Area (GMA) is one such urban centre. The present study assesses the trajectories of LULC change using Landsat imageries acquired in 1976, 1989, 2002 and 2015. Natural and semi natural vegetated area and artificial and natural water bodies decreased while built-up areas, cultivated and managed areas, and natural and semi natural non-vegetated areas increased. The built-up area increased from 23.9 in 1976 to 115.1 km² in 2015 becoming the dominant land cover class accounting for 41.8% of the total geographical area. During this period, natural and semi natural vegetated land were reduced by 88.9 km² at an annual rate of 2.2 km². Over the years there was an increasing trend of built-up land and cultivated and managed areas in the peripheral areas of the city while natural and semi natural vegetated land diminished. Consequently, as in many other developing countries, there is an urgent need for the governmental authorities and other stakeholders to implement effective urban planning policies.
... Nessuna correzione radiometrica è stata applicata. Infatti, benché gli effetti di scattering e assorbimento dell'atmosfera modifichino i valori reali di riflettanza, le differenze spettrali nelle immagini satellitari indicano delle differenze nelle caratteristiche di riflettanza del suolo e della copertura vegetazionale [Tuomisto et al., 2003], assicurando quindi l'individuazione della variabilità ecologica [Chavez, 1986[Chavez, , 1996Cihlar, 2000, Oetter et al., 2001Song et al., 2001;Du et al., 2002]. Una PCA (Analisi delle Componenti Principali) non standardizzata è stata applicata all'immagine Landsat ETM+ in modo da ridurre il sistema multispettrale e rimuovere il rumore aggiuntivo provocato dalla multicollinearità delle bande del visibile [Rocchini et al., 2007]. ...
beta-diversity is defined as the complementarity in species composition between pairs of sites and plays a crucial role in biodiversity management and conservation, since it allows to detect those environmental gradients that functionally act in determining the variation of species composition. From an ecological viewpoint, the decay of beta-similarity principally arises from: (i) a decrease in environmental similarity with distance, which inevitably creates a competition among species with different physiological abilities (niche difference model); (ii) a spatial configuration which creates spatial barriers and thus isolation among habitats, that influences species and gene movement across landscapes. To date, efforts were made to demonstrate the effect of distance on species similarity. However, few tests have been performed at local scale, i.e. at the community level. The aim of this study is to test the distance decay of beta-similarity hypothesis at local scale (10 x 10m plots) considering both (i) spatial distance between pairs of sites: (ii) the ecological variables (elevation, aspect, slope, assolation, spectral reflectance considering both the whole multispectral system of a Landsat ETM+ image and the Near Infrared Wavelength, band 4). beta-similarity decay rates at different thresholds (tau) have been quantified by means of quantile regressions based on exponential models, focusing on the main factors influencing their trends.
... Nessuna correzione radiometrica è stata applicata. Infatti, benché gli effetti di scattering e assorbimento dell'atmosfera modifichino i valori reali di riflettanza, le differenze spettrali nelle immagini satellitari indicano delle differenze nelle caratteristiche di riflettanza del suolo e della copertura vegetazionale [Tuomisto et al., 2003], assicurando quindi l'individuazione della variabilità ecologica [Chavez, 1986[Chavez, , 1996Cihlar, 2000, Oetter et al., 2001Song et al., 2001;Du et al., 2002]. Una PCA (Analisi delle Componenti Principali) non standardizzata è stata applicata all'immagine Landsat ETM+ in modo da ridurre il sistema multispettrale e rimuovere il rumore aggiuntivo provocato dalla multicollinearità delle bande del visibile [Rocchini et al., 2007]. ...
β-diversity is defined as the complementarity in species composition between pairs of sites and plays a crucial role in biodiversity management and conservation, since it allows to detect those environmental gradients that functionally act in determining the variation of species composition. From an ecological viewpoint, the decay of β-similarity principally arises from: (i) a decrease in environmental similarity with distance, which inevitably cre- Rocchini et al. Distance decay della b-similarità: barriere ecologiche o spaziali? 60 ates a competition among species with different physiological abilities (niche difference model); (ii) a spatial configuration which creates spatial barriers and thus isolation among habitats, that influences species and gene movement across landscapes. To date, efforts were made to demonstrate the effect of distance on species similarity. However, few tests have been performed at local scale, i.e. at the community level. The aim of this study is to test the distance decay of β-similarity hypothesis at local scale (10x10 m plots) considering both (i) spatial distance between pairs of sites; (ii) the ecological distance between pairs of sites, measured as Euclidean distance in vector spaces defined by ecological variables (elevation, aspect, slope, assolation, spectral reflectance considering both the whole multispectral system of a Landsat ETM+ image and the Near Infrared Wavelength, band 4). β-similarity decay rates at different thresholds (τ) have been quantified by means of quantile regressions based on exponential models, focusing on the main factors influencing their trends.
... This involves the use of aerial photographs or very high spatial resolution satellite images (VHSRSIs). For example, Cihlar et al. (2000) used this approach to validate AVHRR mosaics with Landsat TM images. Similarly, Goward et al. (2003) validated maps made with MODIS (250 m) and Landsat ETM (25 m) images with IKONOS images (4 m). ...
This review describes the context of the Canadian Wetland Inventory (CWI) and then defines the specifications, establishes the most appropriate dataset, and explores the options for its implementation. The CWI is based on the assumption that a consistent map for all areas of Canada using satellite imagery can be produced for a minimum mapping unit of 1 ha. The CWI will establish the state of land cover for wetlands around year 2000. and the CWI map will classify wetlands according to the following scheme defined in the Canadian Wetland Classification System: bog, fen, marsh, swamp, and shallow water. It will then be possible to roll the map up into simpler classes (i.e.. upland, wetland, open waters, and coastal waters) compatible with other map products. A wide array of datasets is available, and their potential use in the context of the CWI is explored. The best options regarding the mapping method and the evaluation of the map products are both described, keeping in mind that the most suitable method must strike a balance between methodological advances and practical considerations. This review places the various limitations associated with the CWI in perspective and supports several of the CWI specifications; it should also facilitate selection of a strategy tailored to its implementation, in particular for the classification method and the evaluation of the map.
... Purposive sampling of satellite images has also been proposed recently (Cihlar et al., 2000). Purposive sampling is a subjective selection with some restriction that insures that the sample is balanced. ...
Sampling satellite images presents some specific characteristics: images overlap and many of them fall partially outside the studied region. A careless sampling may introduce an important bias. This paper illustrates the risk of bias and the efficiency improvements of systematic, pps (probability proportional to size) and stratified sampling.A sampling method is proposed with the following criteria: (a) unbiased estimators are easy to compute; (b) it can be combined with stratification; (c) within each stratum, sampling probability is proportional to the area of the sampling unit; and (d) the geographic distribution of the sample is reasonably homogeneous. Thiessen polygons computed on image centres are sampled through a systematic grid of points. The sampling rates in different strata are tuned by dividing the systematic grid into subgrids or replicates and taking for each stratum a certain number of replicates.The approach is illustrated with an application to the estimation of the geometric accuracy of Image2000, a Landsat ETM+ mosaic of the European Union.
p>Although soft classification analyses can reduce problems such as those associated with mixed pixels their accuracy is often low. The key aim of this research is to investigate the ways to increase the accuracy of soft classification, the factors that impact on soft classification and its implications for the real world applications.
Four possible methods for combining soft classifications to increase classification accuracy were assessed. All four ensemble approaches were found to increase classification accuracy. Relative to the most accurate individual classification, the increases in overall accuracy derived ranged from 2.20% to 4.45%, increases that were statistically significant at 95% level of confidence.
The impact of intra-class spectral variation on the estimation of sub-pixel class composition was investigated. Results showed that the nature of intra-class variation has a negative impact on the accuracy of sub-pixel estimation as it opposed the assumption that a class can be represented by a single spectral end-member. It was suggested that a distribution of possible class compositions could be derived from pixels instead of a single class composition prediction.
The impacts of intra-class spectral variation on the use of soft classification for super-resolution mapping were assessed. It was apparent that the accuracy of the soft classification and super-resolution mapping declined as the degree of intra-class variation increased.
Finally, a possible method to reduce the impacts of intra-class spectral variation on sub-pixel classification was investigated.</p
En las zonas áridas de México habita la candelilla (Euphorbia antisyphilitica), especie con importancia social y económica, pero cuya disponibilidad no está bien definida. El objetivo de este trabajo fue estimar su distribución potencial y abundancia en el norte del estado de Zacatecas. Para la distribución potencial se realizó un modelado mediante el algoritmo MaxEnt®, donde se usaron 18 registros de presencia: 8 históricos y 10 propios, así como 27 variables predictivas. Se cotejó en campo la presencia mediante 29 puntos aleatorios en el área con distribución potencial y otros 19 fuera de ella. La densidad poblacional se estimó mediante parcelas, se midió la talla de los ejemplares y se consideraron las variables: tipo de vegetación y de suelo, altitud y pendiente del terreno y se realizó la prueba de Kruskal-Wallis. El modelo presentó buena predicción (AUC = 0.920), donde 11 variables contribuyeron con 82.1% en la distribución potencial y las más importantes fueron: tipo de vegetación, exposición, pendiente, altitud y cobertura vegetal. La distribución potencial se encontró en 19.2% del total del área de estudio; la densidad poblacional fue de 295 767.3 individuos por kilómetro cuadrado, influida significativamente por el tipo de vegetación y altitud. La talla de las plantas fue significativamente menor en pendiente escarpada. En 37.9% de los puntos de validación con distribución potencial hubo resultados positivos de presencia de la especie, sin embargo, en 10.5% fuera del área de distribución potencial también apareció. Se concluye que mediante la utilización del algoritmo MaxEnt® se puede modelar la distribución potencial de plantas silvestres, como la candelilla; la distribución potencial fue discontinua y menor a 20%.
Information on the spatial distribution of dominant tree species is important as input or validation data in large scale ecological studies, such as carbon budget estimation, biodiversity assessment, and vegetation dynamic modelling. We used a 1-km resolution land cover map of Canada produced from 1998 SPOT VGT satellite data as the base map. Fractions of coniferous needleleaf or deciduous broadleaf forests within each 1-km pixel were then estimated by developing relationships with climate using land-cover maps from Landsat images selected as a representative sample. The fraction of coniferous/deciduous forest within each 1-km pixel was further divided into dominant species fractions using species composition information at the sub-ecoregion level, derived from statistics in the Canadian Forest Inventory (CanFI 1991/94 version), from narrative descriptions of ecoregions, and from topographical data. A total of 17 Canada-wide maps of dominant tree species groups at 1 km-resolution were produced. The estimates of this study agree well with CanFI data at the ecoregion level where available, and show good correspondence with published range maps of Canadian tree species.
The shape of a river channel is linked to surrounding land use through interacting hydrologic and geologic processes. This study analyzes the relationship between the change in near-stream land use and the shape of the adjacent river channel over time. Three watersheds in the foothills of the Venezuelan Andes that have experienced differing degrees of development were studied to determine river channel width, sinuosity, and position relative to surrounding land use. Change in land use over time was obtained from multiple-date aerial photographs (1946 and 1980) referenced to 1996 Landsat Thematic Mapper (TM) satellite imagery, and verified by field inspection. Measurements of land-use type and amount and river channel morphology from the two dates were made using geographic information system (GIS) methods. The three watersheds differed in the extent of deforestation, the location of remaining forested land, and how much land-use change had already occurred by 1946. Change in river channel morphology was greatest at the most deforested sites. Valley shape and channel constraint also had a discernible effect on change in channel morphology. This study introduces a method for analyzing change in coupled terrestrial-aquatic systems based on multiple-date, remotely sensed data and GIS analysis of spatial properties. The results document human impacts on river channels through a comparison of multiple watersheds over a 35-year time interval.
