Water Level and Morphological Changes of Wetlands in the Poyang Lake Using Sentinel-1 Data

Poyang Lake is the largest fresh lake in China, whose wetland ecological environment and water level change are very complex. Its abundant wetland resources make it a habitat for many migratory birds. Therefore, it is of great significance to study water level and morphological changes of wetlands in Poyang Lake. Synthetic aperture radar can penetrate cloud and mist which is different from traditional optical satellites, it can effectively acquire the reflective characteristics of all objects. The key point in extraction of water area and wetland is threshold selection. An adaptively sample selection method is used to find a perfect distribution with two bounces and then the lowest point between two bounces is the optimal threshold. In recent years, satellite remote sensing has been able to monitor changes of wetland water environment and ecology on a large scale. InSAR technique makes up for the shortcomings in traditional hydrological observation of water level such as few sampling points, long observation period, high monitoring cost and unobservable areas. In this paper, the water or wetland area and water level change in Poyang Lake are obtained from two products of Sentinel-1 data separately. Ground range detected (GRD) images were used to get morphological changes of water and wetland with the adaptively sample selection method, it shows a good application: (1) the area covered by water became largest in July and August; (2) the area of wetland decreased gradually from January to June and the area of wetland showed an opposite trend from September to December. Single look complex (SLC) images were used to get water level change with InSAR technique, it also can be concluded that: (1) the biggest water level change is from July to August, and water level changes between other months showed little differences in value but more differences in spatial distribution; (2) the boundary of water level changes is basically consistent with the boundary between water body and wetland. The results are of great significance for the monitoring and regulation of the water ecological environment of Poyang Lake wetland.