Influence of the vegetation on a VHF radio link over an irregular terrain

This paper deals with the study of radio wave propagation over irregular and woody terrain. We characterize the received signal (power and spatial fluctuations) before, into and outside the forest. We describe first the experimental study and give some results about spatial fluctuations of the received signal. We give the experimental procedure to get a reliable value of the received power with a small number of measurement points. In order to evaluate the influence of the irregular terrain, we use Hufford's (1952) integral equation as a reference model which give accurate results with an open terrain. The electromagnetic field can be evaluated for woody paths by considering that the forest is a dielectric slab diffracting the incident wave. We evaluate the electromagnetic field inside the forest in two steps: first, the attenuation factor due to the irregular terrain, without the forest, is obtained with the resolution of Hufford's integral equation. Second, the attenuation factor due to the forest is calculated with the Bloomquist-Ladel model. A comparison between theory and experiments shows that the model gives accurate results.