MEASUREMENTS AND PREDICTIONS OF ATTENUATION AND SCATTER OF MICROWAVE SIGNALS BY TREES

A set of propagation measurements was conducted at a uniformly planted apple orchard to determine the attenuation of radio waves at 11.2 GHz with increasing foliage depth in the signal path. Measurements were also made to examine the level of scattered signals emerging from such media into free space (backscattering) and its dependence on the angular direction of the receiving antenna. Measurements were conducted over the same path in April where the trees were without leaves and in July where the trees were in full leaf. In support of the experimental study, a theoretical model based on the theory of radiative energy transfer for attenuation and scatter predictions was used to assist in interpreting the experimental results. The model considers a plane wave incident from an air halfspace upon the plane interface with a vegetation halfspace. The vegetation medium is treated as a statistically homogeneous random medium of discrete, lossy scatterers. A comparison of experimental results and theoretical predictions is also presented.