Application of passive microwave and optical signatures to monitor submerging of vegetation due to floods

Abstract

In this article, passive microwave observations in synergy with optical data are exploited to monitor floods and estimate vegetation submerging. The selected site is Sundarban Delta, at the borders between India and Bangladesh. The area is subject to severe monsoon in summer, producing heavy floods and vegetation submerging. Because of their high spatial resolution, Moderate Resolution Imaging Spectroradiometer (MODIS) signatures are used to evaluate the coverage fractions of bare soil, vegetated fields, and permanent water. Multifrequency Advanced Microwave Scanning Radiometer Earth Observing System (AMSR-E) signatures are used to monitor vegetation submerging during monsoon. Results are compared with ground measurements of water level and plant biomass in both agriculture areas and wetlands. Previous studies indicated that, during monsoon, there is a clear effect of brightness temperature decrease and polarization index increase in the C, X and Ka bands over the areas affected by floods. X band data prove to be particularly useful since the sensitivity to flood effects is appreciable and the spatial resolution is better than at C band. In this article, the vegetation submerging effect is estimated with the aid of a radiative transfer model. In the pre-monsoon season, the retrieved value of emerged biomass is close to that of the measured total biomass. During monsoon, it is estimated that up to 3 kg m−2 of vegetation biomass is submerged by flood. For both agricultural fields and wetlands, obtained results are consistent with ground measurements of water level.