Sensitivity analysis of C & Ku-band scatterometers for river water level estimation

Abstract

Water level monitoring is essential for analyzing hydrological extremes, environmental flows, and sustainable development and management of water resources. Satellite Altimeters have operationally been used to estimate river water levels (e.g., SARAL-Altika, Jason-2/3, etc.) with poor revisit times (10-35 days). In this current study, we propose a method to estimate river water levels using scatterometer data with 2-days temporal resolution. Sensitivity analysis of radar frequency (Ku and C band) for river water level estimation was carried out. The concept of change in radar backscatter with an increase in soil wetness is used to develop a model function between Basin Water Index (BWI) and observed river stage. High-resolution OSCAT (Ku-band) and ASCAT (C-band) SIR (Scatterometer Image Reconstruction), digital elevation model, and observed water stage datasets have been used in this study. We observed that C-band scatterometer shows better results than Ku-band in terms of R, NSE, and RMSE, which can be attributed to the higher soil wetness sensitivity of the C band compared to Ku-band scatterometers. R ranged between 0.93 to 0.97 for C-band and between 0.89 to 0.95 for Ku-band data. Similarly, NSE ranged from 0.84 to 0.95 for C-band and between 0.56 to 0.95 for Ku-band data over selected study sites in the Brahmaputra river basin. Model accuracy was found to be adequate for monitoring of river stage from a remote sensing platform. This study shows that scatterometer observations can be used for operational water level estimations, which can be useful for water resource management.