Experimental Measurement And Theory Study On Terrain Electromagnetic Scattering

The electromagnetic scattering features of ground and vegetation is researched by combining measurement experiment with theory in this thesis. The fundamental theory of Kirchhoff approximation and small Perturbation approximation is expounded and the influence of surface roughness, dielectric constant on the back scattering features is analyzed. Measurements of the characteristic parameters of the ground, experimental measurement process and the principle of scatterometer measurement are described particularly. The equivalent permittivity of soil and plants is calculated using empirical models, and the influences of different factors on backscattering coefficient of soil are analyzed. The backscattering coefficient of farmland covered with a newborn winter wheat which is taken as a single-layer vegetation model conformed to the spectral index distribution is computed based on Small slope approximation method. And it is compared with the experiment data. Vegetation model, such as the leaves and stems of plants, is simulated by Generalized Rayleigh Nearly (GRN) and its scattering field is calculated. A first-order scattered field of a single cluster of vegetation (Punco grass and Barbed Ma) composed of leaves and stems is calculated by Monte-Carlo method. The total scattering field of a single cluster of vegetation is accounted through coherent superposition of single scattering. The electromagnetic backscattering coefficient of ground surface is calculated with SPM whose Fresnel scattering coefficient is revised because of the impact of surface height and the curvature factor on volume-surface scattering. The backscattering characteristics of vegetation in random distribution are investigated in further based on the study of single cluster of vegetation. The dependence of cluster distribution, distance between clusters, and samples on backscattering coefficient is comparative analyzed. The experiment data is fitted by Experience and exponential model proposed by F.T.Ulaby and M.C.Dobson.The exponential model of electromagnetic scattering features in experimental area is established.