The GFM product output layer Sentinel-1 Observed Water Extent identifies the pixels classified as open and calm water using Sentinel-1 SAR backscatter intensity and is derived using the ensemble flood mapping algorithm. To map water extent pixels for a certain date, the algorithm uses as input the Sentinel-1 data overpass plus offline-generated Sentinel-1 SAR parameters and auxiliary thematic datasets such as Exclusion Mask and topography (e.g., digital elevation models and HAND index). The relative orbit path information, to select the corresponding offline-generated Sentinel-1 SAR parameters, is extracted from the Sentinel-1 Metadata.
All the processing is done at the 20 metres spatial resolution of the Sentinel-1 pre-processed data cube. The Sentinel-1 Observed Water Extent values are described below.
For further information on how the product is generated please check also: https://extwiki.eodc.eu/GFM/PDD/GFMoutputLayers