An Insight into Coherent Backscattering Evaluation Techniques of Prospective Use in High Frequency Polarimetric Radar Image Processing

Abstract

Coherence in multiple scattering is important as it applies to imaging and detection of object in multiple scattering environments. These phenomena may also be used to investigate images of objects obscured by them. The scattering observations using very rough surfaces can provide useful insight into their statistic as they lie outside the range of validity of the standard theories. Recently, there has been growing interest in the phenomenon of backscattering enhancement in the reflection of electromagnetic waves of mm wave range from both atmospheric hydrometeors (rain, snow and precipitation) as well as very rough surfaces (including that of sea and terrain sea). Strong backscattering enhancement of mm waves incident at different incident angles, both in the TE and TM polarizations, was observed experimentally. In the paper a short description of specific techniques used for treating image processing of strongly irregular media is shortly presented. An emphasis is placed on the phenomena of interest in advanced polarimetric radar especially in mm wave range.PACS numbers: 41.20.Jb, 03.50.De Backscattering enhancementBackscattering enhancement phenomena have been observed for many years. It has been sometimes called the "retroreflectance" or the "opposition effect".Recently, more quantitative experimental and theoretical studies of the enhancement have been reported. Watson in [1] noted that the backscattered intensity is twice the intensity of the sum of incoherent multiple scattering and the first-order scattering. De Wolf in [2] showed that the backscattered intensity from turbulence is proportional to the fourth-order moment and approximately twice the multiple scattered intensity.It was explained in [3] that the enhanced peak is caused by the constructive interference of two waves traversing through the same particles in opposite directions. Physicists have also recognized that the transport of electrons in a strongly disordered material is governed by multiple scattering and that multiple scattering leads to "weak Anderson localization" caused by "coherent backscattering". It is then shown that both electron localization in disordered material and electromagnetic (EM) wave localization in disordered materials are governed by coherent backscattering (CB) which is caused by the constructive interference of two waves traversing in opposite directions. One I l corresponds to the wave multiply scattered through many particles, called the "ladder term". The other I c corresponds to two waves traversing through the * corresponding author; e-mail:jerzy.kapelewski@wel.wat.edu.pl same particles in opposite directions. This is called the "cyclical" or the "maximally crossed" term and has the same magnitude as I l in the back direction, but diminishes away from the back direction (Fig. 1). The essence of this division will be highlighted in Sect. 3. Also two waves scattered off the sloped surface interfere constructively in the back direction producing the enhanced peak. The angular width is relatively broad and appro...