Analysis and Reduction of the Uncertainties in Soil Moisture Estimation With the L-MEB Model Using EFAST and Ensemble Retrieval

This letter quantitatively analyzes and reduces the uncertainties of soil moisture retrieval using the L-band microwave brightness temperatures and the L-band Microwave Emission of the Biosphere model. Through a global sensitivity analysis using the method of extended Fourier amplitude sensitivity testing, the crucial parameters are identified at different polarizations and incidence angles. The retrieval uncertainties of soil moisture caused by the observation error, parameter uncertainty, and retrieval strategy are then studied based on an ensemble retrieval and Polarimetric L-band Multibeam Radiometer flight data. The results show that soil moisture retrieval accuracy is determined by both the total sensitivity of each model parameter and the coupling effect between soil moisture and other parameters. Consequently, three-parameter retrieval, including soil moisture, optical depth, and roughness, is recommended. During three-parameter retrieval using observations at three angles, H-polarization is doing better than V-polarization due to its higher sensitivity to the optical depth; a good pre-estimation and lower standard deviation of optical depth will improve the soil moisture retrieval results. Increasing the number of brightness temperature observations by using multiangle and dual-polarized radiometer can obviously reduce the uncertainties caused by observation error, parameter uncertainties, and inversion method.