Study On The Remote Sensing Monitoring Of Wetland In The Dongting Lake Using ENVISAT ASAR Data

ENVISAT ASAR Alternating Polarization images acquired from 2005 to 2006, with diverse polarizations and incident angles, were used for mapping wetland vegetation and the variation of surface water in the East Dongting Lake. This paper was to show the advantages of ENVISAT ASAR data used in remote sensing monitoring of wetland, and figure out the relationship between spatial distribution of wetland vegetation and inundation. The main contents and results of this research were summarized as follows:(1) Based on the analysis of backscattering coefficients, an image which was made up of cross- and like-polarized signals gathered from multi-temporal ASAR data provides a better separation between classes than a combination of like-polarized signals. Meanwhile, this study adopted the tone of filtered images combined with the"Contrast"texture feature based on the GLCM of unfiltered images to form the feature vector. The experimental result showed that the improved scheme has enhanced the performance of classification, on the other hand, in the dry season scene, the texture channels did not improve the separation on this extent as it did in the flooding scene.(2) Landscape metrics were generated from the classification results of the East Dongting Lake covered 3 different periods in 2005, and Phragmites, Miscanthus sacchariflorus, Carex and Phalaris arundinacea were found the dominating species of wetland vegetation in the East Dongting Lake. Although the inundation had impact on submerged plants and bare land, the wetland vegetation, including Phragmites and Carex, which usually spread over middle or high bottomland were barely submerged.(3) A long time series and single polarization (HH) ENVISAT ASAR images were used to detect the variation of water surface in the East Dongting Lake. Based on the backscatter characters of water, generally, it had a smaller backscatter coefficient than other ground objects, and so water can be identified by a threshold easily. Moreover, the max-submersion time index indicated that the persistent land or water bodies took nearly 78.41% of the total area, without the pressure of flood control. But for the rest fluctuating region (21.59%), measures should be taken for flood control and flood fighting. To avoid flood detention and depositional intensification, the planting of Phragmites and Carex should be forbidden in the rest fluctuating region.