Potential of NISAR Mission for Improved Flood Disaster Studies

In the recent decades, microwave Synthetic Aperture Radar (SAR) images have become an integral part for mapping and monitoring flooded areas because of its unique capability of day and- night acquisition and weather independent images. The NASA-ISRO Synthetic Aperture Radar (NISAR) mission scheduled to be launched in the 2022-23 time frame will carry an L-band synthetic aperture radar (SAR) instrument provided by NASA and an S-band SAR instrument provided by ISRO. Both instruments are designed for surface deformation and change measurements that support natural hazard science and for monitoring and assessment of natural disasters such as floods, forest fires, landslides and earthquakes. In India, C-band data from RISAT, RADARSAT and SENTINEL series of satellites is operationally used for mapping and monitoring of floods in near-real time under the DMS Programme of ISRO. This paper investigates the capabilities of the NISAR L &S-band towards science products and flood disaster response. The backscatter response of the flooded waters using multi-frequency L, S and C-band data from ALOS-2 PALSAR, NOVASAR and RADARSAT satellites respectively is analysed for a flood event in Assam in July 2020. It was observed that the flooded vegetation was identified in the L-band due to its capability to penetrate the canopy and was found to be useful for mapping and monitoring the flooded vegetation which helps in crop damage assessment. The backscatter in the open flooded areas for S-band and C-band are relatively close, though some intrinsic variations are observed. The NISAR 12-day repetitive observations augment monitoring of the riverine and coastal flooding more frequently on operational basis.