Flood inundation mapping of the Koshi River basin using microwave remote sensing

Floods are among the most severe natural hazards, causing substantial damage to lives, infrastructure, and economies, particularly in densely populated regions. This study utilizes Synthetic Aperture Radar (SAR) data to map flood inundation in the Koshi River Basin, Bihar, India, during 2023. SAR's all-weather capability enables reliable flood monitoring under cloudy and adverse weather conditions. Sentinel-1 SAR images were processed using SNAP software through radiometric calibration, speckle filtering, terrain correction, change detection, and thresholding techniques to distinguish flooded from non-flooded areas based on backscatter values. District-wise flood inundation maps were generated to quantify the spatial extent of flooding. Rainfall analysis indicated that Khagaria experienced the highest rainfall and, consequently, the greatest flood impact during the study period. The results were validated using topographic information, including elevations, contour lines, water boundaries, and land features. The study demonstrates the effectiveness of SAR-based techniques for accurate, timely flood-extent mapping.