Modeling the Dynamic Effects of Vegetation on Radiowave Propagation

In this contribution we use available measurements at 2.45, 5.25, 29 and 60 GHz to study the dynamic effects of vegetation on propagating radiowaves. The complex responses of a tree to induced wind force has been studied, and used to explain different phenomena observed in measurement results. Generally, the power spectrum of the received signal through vegetation has lowpass characteristics, and the effects of swaying tree components are manifested as spectral peaks in the power spectrum of the received signal. Radiowaves scattered from these swaying tree components have a time varying phase changes which results in fading of the received signal. Furthermore, due to further dissipation of the wind energy by the interaction of tree crowns, less signal variation is to be expected from a grove of several trees than from a single/few tree(s). The Ricean K- factor for different wind conditions has been estimated from measurements. In addition, by utilizing a lowpass filter and a mass-spring system, a new simulation model for generating signal fading due to a swaying tree has been developed. Depending on the wind speed and physical characteristics of the tree, the new model can be used for simulating signal fading due to a swaying tree with similar dynamical and statistical characteristics as those observed from measurement results.