Application of an extended IEM to multiple surface scattering and backscatter enhancement

In the late 1980's backscattering enhancement and strong depolarization of waves scattered from randomly rough Gaussian surfaces with large rms slopes were observed in optical and millimeter wave measurements. It was noted that backscattering enhancement was most prominent, when the surface rms slope was of the order of unity, a condition under which multiple surface scattering may dominate. In this study an extended IEM model which includes surface multiple scattering called integral equation model with multiple scattering (IEMM) is applied to interpret this phenomenon. According to this model the conditions for significant multiple surface scatter to occur are (1) the normalized surface height k sigma > 1 and (2) the surface rms slope > 0.5. In the analysis of multiple scattering from very rough surfaces it is found that there is a sharp but small peak in the specular direction also. This observation comes directly from the IEMM model and is partially confirmed by the data reported by Ishimaru. Further comparisons of IEMM with experimental data acquired from very rough surfaces show agreements within a dB in bistatic scattering including backscattering enhancement.