The GFM product output layer Exclusion Mask indicates the pixel locations where the SAR data could not deliver the necessary information for a robust flood delineation, due to the combined deleterious effects of the following “static” factors:
- No sensitivity in flood mapping
- “Water-look-alikes”
- Strong topography
- Radar shadows
For generation of the Exclusion mask, the GFM product implements various methods that address the identified problems of SAR-based flood mapping. The parameter database stores for all locations on pixel basis the areas excluded by the four effect groups, with the radar shadow layer per local Sentinel-1 orbit configurations (up to six per location). During NRT operation, the relative orbit is determined from the S-1 metadata, and the respective Exclusion Mask layers are subset to the extent of the processed Sentinel-1 scene and form a single binary mask for exclusion areas. The Exclusion Mask layer values are described below.
As no-sensitivity is a problem leading often to an underestimation of floods rather than to overestimation (e.g., in urban areas), the no-sensitivity -masking is only applied to pixels that are classified as non-flooded, whereas pixels classified as flooded are kept unmasked. Any no-data areas from the flood mapping algorithm are forwarded to this layer and added as no-data values.
For further information on how the product is generated please check also: https://extwiki.eodc.eu/GFM/PDD/GFMoutputLayers