FURTHER STUDY OF RAINFALL EFFECT ON VHF FORESTED RADIO-WAVE PROPAGATION WITH FOUR-LAYERED MODEL

In this paper, rainfall efiect on the VHF radio-wave propagation in a tropical forest is further studied in details. Theoretical study and experimental investigations are performed with the help of a four-layered model for forested environment. It is found that the lateral wave traveling along the air-canopy interface, the direct waves, and the ground re∞ected waves are the main modes for VHF radio-wave propagation in forest. The rainfall can afiect these propagating waves to difierent extents. Especially, due to the increase in the dielectric permittivity of the wet canopy layer by rain water, the time of arrival of the direct wave traveling through the canopy layer can be delayed signiflcantly. Finally, the dielectric permittivity for the wet canopy layer under difierent rain events is evaluated empirically.