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 th at backscattering enhancement was most prominent, when the surface rms slop e was of the order of unity, a condition under which multiple surface scatt ering may dominate. In this study an extended IEM model which includes surf ace multiple scattering called integral equation model with multiple scatte ring (IEMM) is applied to interpret this phenomenon. According to this mode l 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 f ound that there is a sharp but small peak in the specular direction also. T his observation comes directly from the IEMM model and is partially confirm ed by the data reported by Ishimaru. Further comparisons of IEMM with exper imental data acquired from very rough surfaces show agreements within a dB in bistatic scattering including backscattering enhancement.