In this thesis the radar backscatter response of natural rough surfaces is studied for the purpose of retrieving the soil moisture and surface roughness parameters from microwave radar observations. This investigation, which included theoretical, numerical and experimental components, has lead to the development of a hybrid scattering model for predicting the polarimetric radar response of bare soil surfaces. This model is then used as a basis to develop an inversion algorithm for the soil moisture and surface roughness parameters based on the measured polarimetric radar backscatter when the radar parameters are known.; Classical scattering models, such as the small perturbation method and the Kirchhoff approximation (the physical optics and the geometrical optics models), are re-examined and an improved Kirchhoff approximate solution is derived. The analytical solutions based on the classical scattering models are examined by comparing them to the results obtained from exact numerical simulations and extensive experimental observations. A Monte Carlo method is used in conjunction with the method of moments to provide a scattering solution for one-dimensional conducting surfaces. Also, the effect of dielectric inhomogeneity in a soil medium is studied by developing an efficient numerical technique for one-dimensional inhomogeneous dielectric rough surfaces. Unfortunately, the numerical simulation for a one-dimensional surface does not produce depolarization and its prediction for co-polarized components are much different from real surfaces that are two-dimensional. Therefore, careful controlled experiments are conducted to study surfaces with two-dimensional roughness.; An accurate technique for measuring the polarimetric backscatter from distributed targets was also developed. Using this method, an extensive experimental data set are acquired from bare soil surfaces with many different roughness and moisture conditions at microwave frequencies. The scattering behavior based on these experimental observations and the results derived from the theoretical and the numerical studies have been combined to develop the hybrid (semi-empirical) scattering model for the backscattering coefficients, {dollar}sigmasbsp{lcub}vv{rcub}{lcub}rm{lcub}o{rcub}{rcub}, sigmasbsp{lcub}hh{rcub}{lcub}rm{lcub}o{rcub}{rcub}, sigmasbsp{lcub}hv{rcub}{lcub}rm{lcub}o{rcub}{rcub}{dollar}. This model and its inversion algorithm are tested against many independent data sets, and excellent agreement is obtained.
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