25. Application of Active Space-Borne Microwave Remote Sensing in Flood Hazard Management

Globally, floods are attributed to be one of the leading natural hazards responsible for recurrent major economic losses, population affected, and mortality. The rapid assessment of flood hazard dynamics at regional scale during flood crisis is one of the few elements which is required by the agencies involved on ground for relief and rescue operations. Due to the weather-independent and day and night acquisition capability offered through microwave sensors, space-borne remote sensing for flood hazard management has undergone a paradigm change. Today, globally data from synthetic aperture radar (SAR) has emerged as invaluable source for monitoring flood hazard. From demonstrating the proof of concept in its initial launch campaigns, the SAR technology has matured to be competent enough to provide operational support for major flood disasters. In recent times, the continuously streaming of free SAR datasets from Sentinel-1 mission and together with emergence of advanced cloud-based computing and processing technologies like the Google Earth Engine (GEE), automated, and quasi-real-time flood mapping services have evolved. The future missions like the NISAR in conjunction with Sentinel-1 C-band data will help in providing more accurate and faster response during flood crisis and see application of SAR data grow multi-fold in coming years for flood hazard mitigation. This chapter attempts to provide a broad overview of the active microwave remote sensing for flood hazard studies. The first part of the chapter discusses about the interaction of the SAR signal for flooding in open, vegetated, and urbanized areas, followed by the role of the sensor parameters like the wavelength, polarization, and incidence angle on the backscattering of SAR signal. The latter half of the chapter discusses about the flood mapping techniques, SAR satellite mission contributing to flood hazard mapping, various applications of SAR derived flood hazard information, the Indian nationwide near-real-time (NRT) flood hazard mapping under ISRO DMS program, and the emergence of Web-based cloud computing techniques and open-source data policies revolutionizing the flood hazard mitigation activities.