Abstract
The motivation of this present study is to investigate the relative contributions of the three major scattering interactions from a vegetative medium, namely the dif‐ fuse scattering contribution by the vegetation volume, the diffuse surface‐volume interactions and the direct surface scattering contribution. Such analysis allows us to study the conditions under which the total backscatter can be obtained by simple theoretical models that add incoherently the volume backscatter and the surface backscatter without taking the surface‐volume interactions into consideration. Electromagnetic backscattering from a vegetative medium is modelled based on the Monte Carlo technique. The vegetative model consists of two layers: the top layer contains a mixture of randomly‐oriented discrete disk‐shaped scatterers and cylindrically‐shaped scatterers, representing the leaves and stems of the vegetative canopy respectively; while the bottom layer is a semi‐infinite space representing the ground. The ground‐vegetation interface is characterized by a Kirchhoff rough surface based on the stationary‐phase approximation. Numerical illustrations of the relative contributions to the microwave backscatter cross‐sections from volume‐volume interactions, surface scattering and surface‐volume interactions at different frequencies are given. It is found that at high frequency (>6 GHz) and large incident angle (>50°), volume‐volume scattering process is the dominant scattering mechanism for backscatter. At low frequency and for near‐vertical incident angle, contribution to main‐polarized backscatter is dominated by direct surface scattering; while surface‐volume interaction is the major backscatter mechanism for cross‐polarized return. Thus, in general, the surface‐volume interaction should not be neglected for L‐ and C‐band range of frequency. Also illustrated are the effects on backscatter coefficients by volume fraction and moisture content of vegetative components; as well as effect of soil moisture content.