Application potential of GF-4 satellite images for water body extraction

Water body extraction plays an important role in flood control and the utilization of water resources. With the launch of China’s first high-resolution (50m) geostationary optical GF-4 satellite at the end of December 2015, the wide-swath (400km) and high-frequency (up to minutes) imaging capabilities have been greatly improved, which provides new possibilities for rapid and accurate water body monitoring. To explore the potential of GF-4 satellite in water body monitoring, this paper proposes a water body extraction method based on the temporal variability of near infrared (NIR) spectral features. For a series of preprocessed and coregistered GF-4 images, one of them is chosen as the base image whose NIR band (B5) thresholding is firstly applied to eliminate most of the non-water regions. Then, for each pixel, the variance of B5 radiance values of all images is calculated to obtain a variogram, and pixels whose variogram values are larger than a certain threshold given by the OTSU algorithm are further eliminated. Finally, the final water body extraction result can be obtained after post-classification processing. To evaluate the efficacy of the proposed method, two groups of GF-4 datasets with complex water distribution are selected in the areas of the middle and lower reaches of Yangtze River in China. Experimental results demonstrate that thanks to the high-frequency and high-resolution characteristics of GF-4, the proposed method can extract more tiny waters and effectively remove built-up areas, and is superior to the extraction accuracy of water index way by about 4%.