Vegetation Attenuation Combined with Propagation Models versus Path Loss Measurements in Forest Areas

This paper examines the suitability of some propagation models for forest environments. To that end, the vegetation attenuation is augmented to the appropriate propagation models. The vegetation attenuation models considered here are the maximum attenuation (MA) model and the foliage attenuation model which were recommended by the International Telecommunications Union (ITU-R). The propagation loss models considered here are: Free space model, plane earth model, modified Okumura-Hata model for open area (or shortly: modified Hata), Lee model for free space area, and Lee model for open area. These models, combined with the vegetation attenuation, are compared with the experimental measurements performed in the forests of Nigeria at 92.1 MHz. The comparison reveals that the ITU-R foliage attenuation model is not suitable to predict the propagation loss between the radio transmitter with height of 130 m and the receiver located near the forest ground. On the contrary, the ITU-R maximum attenuation (MA) model shows much better accuracy. Specifically, the root mean square error (RMSE) between the ITU-R foliage predicted and measured data reaches up to 93.4 dB. However, the RMSE between the data predicted by the maximum attenuation (MA) ITU-R Lee model for free space and the measured data is only 5.6 dB. These results indicate that the vegetation loss is mainly due to the tree canopy rather than the foliage loss, and the direct ray is the major contributor to the received signal in this forest area.