Delineating lakes and enclosed islands in satellite imagery by geodesic active contour model

The objective of the present paper is to develop a new method for delineating lakes and enclosed islands from shuttle radar topography mission (SRTM) digital elevation model (DEM). The Thousand-Island Lake in China is chosen as the study site. DEM may have missing values or be inaccurate over water bodies. Thus, it is not trivial to delineate the shorelines of lake directly from DEM. We achieve this objective by overlaying the boundary derived from the Landsat image of the same area. Unlike traditional water body delineation techniques, e.g. the band ratio method, which make use of physical quantities, we only use the colour information from Landsat ETM+ band 7, 4 and 2. The main reason is that the colour information is the only resource available for most publicly available satellite data such as the maps from Google Earth. Thus, it is necessary to develop a method depending on only colour information. In the Landsat image, a discrimination function to determine whether a pixel belongs to the lake area is obtained by studying sample pixels chosen from the lake area. The delineation of shorelines is an evolutionary process. The evolution equation is derived according to the active contour model and the discrimination function. The initial contour is inside the lake and expands according to the evolution equation. The evolving curve converges to the boundaries of the lake efficiently with a satisfactory result. Finally, the shorelines are overlaid on the DEM according to latitude and longitude. Our geodesic active contour method is a general one, and could be used to delineate objects of interest such as oil slicks and burn scars in satellite images.