Improvements in flood monitoring by means of interferometric coherence

摘要

SAR images has already been successfully exploited for the detection of changes in a scene. Being the backscatter intensity affected by the presence of wind fields, water and flood identification could be unreliable, unless weather information are integrated. On the contrary, interferometric coherence, usually low in presence of water, is not sensitive to weather conditions. As a consequence, the additional information provided by the absence of coherence over water should allow a more accurate identification of flooded areas. A qualitative and quantitative evaluation of the improvement that could be obtained by exploiting interferometric data has been performed. The data set is composed by interferometric pairs acquired by the ERS-1/ERS-2 satellites before and during the Yangtze River flooding occurred in China in summer 1998. Starting from these data, several features have been computed and associated to the channels of an RGB image, in order to obtain an intuitive interpretation of the data content and an easy identification of the flooded areas. The results show that, in order to correctly highlight the flooded areas the best combination of features includes the coherence difference between the acquisitions before and during the flooding, the backscatter intensity in the reference period and the coherence computed during the flooding.