Theoretical and experimental study of attenuation and scatter of microwave signals by trees

The authors present the results of an experimental investigation conducted at 11.2 GHz to examine the attenuation rate of microwave signals propagating through trees and to quantify the backscattered signal level emerging from a vegetation medium into free space. Measurements were carried out at an orchard consisting of a uniform plantation of apple trees of the same growth with a clearance in the foreground to enable radio wave illumination. The measurements were repeated over the same path in April where the trees were without leaves and in the middle of July where the trees were in full leaf. Experimental results are compared with theoretical predictions based on the theory of radiative energy transfer (transport theory). This theory allows multiple scattering to be taken into account. The model adopted is similar to that suggested by F. Schwering et al. (see IEEE Trans. Geosci. Remote Sens., vol.16, no.3, 1988)