Detection of urban flood inundation using RISAT-1 SAR images: a case study of Srinagar, Jammu and Kashmir (North India) floods of September 2014

Microwave data from SAR (synthetic aperture radar) sensors are used extensively in providing operational support for riverine floods, unlike for urban flood disaster. Current approaches for flood mapping using SAR basically aim at detecting for regions of low backscatter due to specular reflection from water surface. However, flooding in urban areas may appear bright in SAR images, because of the enhancement of the double-bounce effect. The present communication presents a case study of the use of moderate-resolution C-band SAR images from Indian Remote Sensing Satellite RISAT-1 to assess the changes in backscattering coefficient (sigma(0)) values (flood sigma(0 )- non-flood sigma(0)) for catastrophic floods of September 2014. SAR images considered for evaluation are with similar acquisition parameters (orbit, look direction, incidence angle, polarization, imaging mode, resolution, and acquisition time) to have a consistency in comparison of backscatter values. From the backscattering coefficient (sigma(0)) comparison analysis and visual inspection between pre-flood and flood duration images, it is observed that there is a significant increase in the sigma(0) values of about 8.0 dB and corresponding increase in the tonal brightness of flooded locations. The areas identified with high backscatter response are also validated for flooding through high-resolution Pleiades (spatial resolution 0.5 m) optical satellite data and ground information from open sources. The observations made from this study highlight the fact that moderate-resolution SAR images could be an important source in indicating urban flooded areas during rapid response.