Effects of spatial heterogeneity of soil parameters on soil moisture retrieval from passive microwave remote sensing

Soil moisture is an important variable in the process of water and energy exchanges at the land surface. Passive microwave remote sensing techniques have great potential for its frequent coverage, low data rates, and simpler data processing, but with poor spatial resolution, which resulted in sub-pixel heterogeneity. To study the effect of spatial heterogeneity of soil parameters on the retrieval of soil moisture, HI and EI were defined as the description of parameter´s sub-pixel heterogeneity and the error of soil moisture retrieval, respectively. This paper firstly simulated different sub-pixel heterogeneities of each parameter, which were used as the input of the radiative transfer (RT) model, and then compared the soil moisture results retrieved by taking heterogeneity into account with that neglected the heterogeneity, seeking the relationship between those parameters´ heterogeneity and the error of soil moisture retrieval. Finally, the conclusion was validated by two exact field experiments based on a Truck-mounted Multifrequency Microwave Radiometer (TMMR). It can be concluded that the RT model has enough accuracy to this study. The simulation analysis and field experiment reveals that there´s a good relationship between the heterogeneity index and error index. The EI increased with HI grow up. However, the absolute error resulted by the spatial heterogeneity of soil moisture in bare soil is negligible.