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 a lso made to examine the level of scattered signals emerging from such media into free space (backscattering) and its dependence on the angul ar direction of the receiving antenna. Measurements were conducted ove r the same path in April where the trees were without leaves and in Ju ly where the trees were in full leaf. In support of the experimental s tudy, a theoretical model based on the theory of radiative energy tran sfer for attenuation and scatter predictions was used to assist in int erpreting the experimental results. The model considers a plane wave i ncident from an air halfspace upon the plane interface with a vegetati on halfspace. The vegetation medium is treated as a statistically homo geneous random medium of discrete, lossy scatterers. A comparison of e xperimental results and theoretical predictions is also presented.