Abstract: The accurate extraction of surface water is an important basis for studying the changes of quality and quantity for surface water. Sri Lanka is one of the most important participating countries along "21st-Century Maritime Silk Road".Rainfall is abundant in Sri Lanka. However, due to uneven spatial and temporal distributions of the rainfall, people in Sri Lanka have a long-term difficulty in using water. Study on surface water is helpful for solving the problem of people's livelihood in Sri Lanka. There are a large number of small reservoirs and ponds scattered throughout the country,but it is difficult to extract small area water which is affected by surrounding environment. In this paper, the accuracies and existing problems of water extraction methods, such as single-band method, water body index method, and supervised classification method, were compared and analyzed based on Sentinel 1/2 satellite image in July 2017 in eastern Sri Lanka. The analysis results show that the normalized difference water index (NDWI) method has the highest accuracy with a classification accuracy of 94%.

Key words: Sentinel-1/2, surface water extraction method, NDWI