The finite volume time domain (FVTD) method is applied to electromagnetic wave scattering from random rough dielectric surfaces. In order to gain a better understanding of physics of backscattering of microwave from rough surface, this paper treats both horizontal and vertical polarizations especially at low- grazing angle. The results are compared with those obtained by the Integral equation method and the small perturbation method as well as with the experimental data. We have shown that the present method yields a reasonable solution even at LGA. It should be noted that the number of sampling points per wavelength for a rough surface problem should be increased when more accurate numerical results are required, which fact makes the computer simulation impossible at LGA for a stable result. However, when the extrapolation is used for calculating the scattered field, an accurate result can be estimated. If we want to obtain the ratio of backscattering between the horizontal and vertical polarization, we do not need the large number of sampling points.

This paper describes an individual effect of soil moisture (mg) and surface roughness (hrms) of bare soil on the back scattering coefficient (σ0) at the X-band frequency. The study contributes to the design of an efficient microwave sensor. For this purpose, experimentally observed data was utilized to provide a composite σ0 equation model accounting for individual effect in regression analysis. The experimental data are compared with Small Perturbation Method. It is observed that the X-band gives better agreement up to incidence angle 50 for HH-polarization and 60 for VV-polarization as compared to the C-band. The lower angles of incidence give better results than the higher angles for observing mg at the X-band. The multiple and partial regression analyses have also carried out for predicting the dependence of scattering coefficient (σ0) on mg and hrms more accurately. The analyses suggest that the dependence of dielectric constant (i.e., mg) is much more significant in comparison to surface roughness at lower angles of incidence for both like polarizations. The results propose the suitable angle of incidence for observing bare surface roughness and soil moisture at the X-band. All these data can be used as a reference for satellite or spaceborne sensors.

A new method for measuring the scattering coefficient using a metal-plate reflector was developed in order to provide a non-destructive way for the assessment of microwave materials in free space. By displacing the position of the metal-plate reflector on the specimen to be tested, the incident wave and the scattered wave from the measured area were determined without the influence of extraneous waves such as the direct coupling between transmitting and receiving antennas and scattered waves from background objects. Because the behavior of a metal-plate reflector is similar to that of an optical shutter in optics, our new scattering measurement system enables us to measure both backward- and forward-scattering coefficients of small regions of the specimen for various types of materials in a non-destructive manner. Our study examined the metal-plate size dependence of the complex reflection and transmission coefficients of some dielectric sheet samples. The measured data indicated that the reflection and transmission coefficients of a Bakelite flat plate and Styrofoam sheet were constant for various sizes of metal plates at the X-band.