Calculation of scattered power from random medium layers by using radiative transfer theory for the estimation of moisture in soil by microwaves

The detection of a water content of soil is one of important subjects in civil and agricultural engineering. Microwave remote sensing seems to be a promising detection technique because the microwave properties of moist soil are sensitive to water content. Passive and active microwave remote sensing approaches have been studied. Moist soil, composed of air, soil particles, bound water and free water, may be considered as a dense random medium from a theoretical point of view. We assume moist soil as three layers of random medium with flat interfaces, and investigate the effects of particle distribution density in the depth direction for developing a method for detecting a water content of soil by active remote sensing. In each layer, many water drops or soil particles coated by bound water are randomly distributed. The dense medium radiative transfer equation (DMRT), with coefficients estimated by our method, is used to calculate the scattering cross sections of the layers. We clarify numerically the characteristics of the scattering cross sections by changing the fractional volume of particles in the random medium layers, each layer thickness and the incident angle and polarization of incident waves. We finally discuss the possibility of water detection in soil on the basis of the characteristics.