Remote Sensing of Soil Moisture

Soil moisture, its temporal and spatial variations are influential parameters in both climatic and hydrologic models. With the advent of synthetic aperture radar (SAR) and radar polarimetry, radar remote sensing of soil moisture has attained significant prominence in the past decade. In this study, we are investigating the theoretical, numerical, and experimental aspects of electromagnetic scattering from rough surfaces. In the general case, the microwave backscatter from natural surfaces is determined by three major factors: (1) the roughness statistics of the soil surface, (2) soil moisture content, and (3) soil surface cover. To develop an accurate inversion model for soil moisture we have conducted an extensive experimental measurements of the radar polarimetric backscatter from bare soil surfaces at 1.25, 5.3, and 9.6 GHz over a wide range of moisture conditions and roughness scales. These data set is used for two purposes: (a) evaluation of the prediction accuracy of theoretical surface scattering models such as small perturbation, physical optics, and geometric optic models, and (b) development of an accurate semi-empirical model. Theoretical expressions for the bistatic scattering coefficients of soil surfaces with slightly rough interface and stratified permittivity profile are being developed. The scattering formulation is based on a new approach where the perturbation expansion of the volumetric polarization current instead of the tangential fields is used to obtain the scattered field. In addition to these activities, novel numerical scattering code for rough surfaces based on volumetric and surface integral equations are under development.

Radar Remote Sensing of Soil Moisture