Assessing Envisat ASAR and Sentinel-1 multi-temporal observations to map open water bodies

C-band observations of the SAR backscatter from the Envisat ASAR (2005-2012) and Sentinel-1 (2014-ongoing) instruments are reviewed to understand their suitability to detect of open water bodies. The temporal variability (TV) and the minimum backscatter (MB) of ASAR backscatter were fed to a simple algorithm based on thresholds to obtain an indicator of water bodies globally with a spatial resolution of 150 m. Confusion occurred either in the case of irregular acquisitions of ASAR images or in cold and arid regions where the multi-temporal metrics based on the multi-year ASAR dataset were often similar to values obtained over open water bodies. With Sentinel-1, there are clear chances to improve the mapping of water bodies considering the dual-polarization capability, the higher spatial resolution and the more consistent observation strategy. First examples from a test site in Sweden show that average and minimum cross-polarized backscatter are suited for water body mapping.