ALOS-2 and Sentinel-1 Backscattering Coefficients for Water and Flood Detection in Nakhon Phanom Province, Northeastern Thailand

Abstract

Synthetic Aperture Radar (SAR) plays an important role in disaster management, such as in flood area monitoring, as it can withstand severe weather or the rainy season. The main objective of this study was to investigate the potential of ALOS-2 (L-band) and Sentinel-1 (C-Band) SAR data for water and flood mapping. This study used ALOS-2 and Sentinel-1 to detect water areas from pre- and mid-flood events in Nakhon Phanom Province, Thailand. Water areas were determined via the thresholding method. The study assessed different polarizations of ALOS-2 (HH, HV) and Sentinel-1 (VH, VV) characteristics, as well as non-filtered and filtered images in the detection of water areas. Water extension detection from the optical sensor (Sentinel-2) was compared with SAR results. Water detection by ALOS-2 and Sentinel-1 images were independently observed with less cloud effect and showed good agreement with Sentinel-2. ALOS-2 HH demonstrated higher accuracy (92.46%) than ALOS-2 HV. Sentinel-1 VV provided the highest accuracy (95.45%) among all the results analyzed. The differences between L-band and C-band results accounted for 8.8% of the study area, with major differences appearing in the paddy fields. Water and flood detection by satellite images provided not only spatial information but also temporal dimensions. The results of this study can help inform decision-making in future flood mapping and disaster management.