A Study of Fresenel Scattered Field for Non-Spherical Discrete Scatterers - Abstract

Abstract

Scattering from a non-spherical scatterer at microwave frequency has always been an interesting electromagnetic problem. In this paper, the Fresnel zone scattered field of three types of non-spherical discrete scatterers, namely disks, needles and cylinders, are studied. Scatterers of these shapes are commonly used to model the leaves, branches and trunks of vegetation canopy. Conventionally, a far field approximation of the scattered fields from these scatterers is applied in the microwave scattering models to account for the interactions among the scatterers. However, when the scatterers are in the Fresnel zone of one another, it is necessary to consider the additional interaction effect among the scatterers. This effect is considered by including two types of corrections into the far field scattered fields of these scatterers : amplitude correction and Fresnel phase correction. The amplitude correction is considered by including the near field amplitude term of the scattererd fields whereas the Fresnel phase correction is obtained through the consideration of the higher order terms in the phase of the scattered fields. It is found from the theoretical analysis that the effects of these two corrections to the scattering cross section of the scatterers are dependent on the frequency, density, size and orientation of the scatterers. Good agreement is obtained between the theoretical results and the measured backscattering cross sections of rods, disks, birch stick and aspen leaf.