On Randomly Absorbing and Scattering Surface Layers

Radar wave scattering on natural surfaces by randomly distributed irregularities of the absorption and phase properties superimposed on an average medium is studied. Two simple models are regarded replacing the real medium by a plane one with continuous distribution of phase and absorption and one with discrete absorbing celis. The scattered radiation contains a coherent (specular) part which is dependent on the antenna size to wavelength ratio and a random (diffuse) part. The angular width of the diffuse component is given by the ratio of mean dimension of the irregularities and the wavelength. The computed scattering patterns are compared with measurements. The resulting absorption of the surface layer determines the albedo and thus the emissivity. Reasonable assumptions yield backscatter and emission values fitting favorably to typical observations. The importance of the random absorption for the diffuse scattering and emission processes becomes evident.