Radar backscatter inversion techniques for estimation of surface soil moisture: EFEDA-Spain and HAPEX-Sahel case studies

Soil moisture is considered to be the link between the water and energy balance at the land surface. The extraction of information on soil moisture from remotely sensed data, especially from microwave instruments, has always received a lot of attention. Most methods that are used to extract this information are empirical in nature. In this paper, a semiempirical model from Y. Oh et al., (1992) and a numerical inversion of the Integral Equation Method (IEM) model, introduced as "INVIEM," are applied to retrieve soil moisture over bare soil surfaces from active microwave data. The two models are compared using data from the Jet Propulsion Laboratory (JPL) air synthetic aperture radar (AirSAR) taken during the EFEDA-Spain'91 experiment and ERS-1 data from the HAPEX-Sahel'92 experiment. The comparison is performed within a general framework to estimate soil moisture from radar data, describing all necessary steps. The range of soil moisture values estimated by the INVIEM model, using the AirSAR and ERS-1 data, is in agreement with the soil moisture variation found in the field.