A physically based statistical methodology for surface soil moisture retrieval in the Tibet Plateau using microwave vegetation indices

Surface soil moisture is the key state variable in various hydrological processes. A physically based statistical methodology for surface soil moisture measurement in the Tibet Plateau was developed in this study. The approach was established based on theoretical relationships from the derivation of physical models. The methodology was calibrated using statistical analysis of a large data set obtained during a long-term experiment in Tibet. The procedure was conducted using multichannel brightness temperature observations from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E). The most interesting results of this study were that the newly developed microwave vegetation indices (MVIs) are a function of vegetation water content or vegetation transmissivity. The B parameter of MVIs decreased with increased vegetation water content but increased with increased vegetation transmissivity. This enabled the use of MVIs for the correction of vegetation effects in soil moisture inversion. The methodology was tested against several experimental data sets collected from Tibet and was shown to be an effective method of soil moisture retrieval for areas with sparse vegetation coverage. The results also provided a complementary data set of soil moisture for hydrology and climatology studies in the Tibet Plateau.