Backscatter from scattering cells located in a random medium

Abstract

Certain diagnostic methods, based on electromagnetic backscatter phenomena, seek to provide information on selected scattering volumes that are part of a larger randomly fluctuating medium. Under these circumstances, the effects of the fluctuating medium on the signal passing to and from the scattering cell cannot be ignored. Inhomogeneities in the background refractive index may also significantly affect the characteristics of the backscattered signal. Assuming large scale, small amplitude, refractive index fluctuations, the present study explores the influence of the propagation path on the scattering cross section, as well as on the first and second moments of the temporal spectrum of the backscattered signal. In a homogeneous background, fluctuations are found to provide the same mean frequency shift as the Born approximation, but to enhance the second Doppler moment. In an inhomogeneous background, the latter effect may be overshadowed by deterministic refraction, especially for scattering volumes located far from the source. These aspects are illustrated by application to a radially stratified plasma column.