Flood Detection in Urban Areas: Analysis of Time Series of Coherence Data in Stable Scatterers

The utility of synthetic aperture radar (SAR) data to produce flood delineation maps is well established. However, flood mapping still represents a challenge in urban settlements, because the radar signatures of flooded urban pixels are generally ambiguous. As a matter of fact, flood mapping algorithms generally do not consider urban areas, thus producing a lot of missed detection errors. Recent studies demonstrated that SAR Interferometry (InSAR) represents a suitable tool to at least mitigate this problem. Following these studies, here we analyze time series of complex coherence data in stable scatterers, i.e., pixels exhibiting high backscatter combined with high temporal stability. Our idea is based on the fact the water surfaces show no coherence in a repeat-pass interferogram, so that a decrease of coherence may occur even for stable scatterers if floodwater is present in a resolution cell. The analysis was performed considering the floods that hit the city of Alicante (Spain) in March 2017. This event was observed by Sentinel-1 in Interferometric Wide Swath mode.