RF propagation through vegetation with time-varying moisture

Six broadband measurements were made of the transmission at 3-4 GHz between two horn antennas 30 cm above the ground through 80 cm tall grass. Water was sprayed over the tall grass, and the variation in transmission was captured as the water evaporated. The results show an increase in transmission through the wet grass of 6.5 dB at an 8 m distance. This partially supports our hypothesis that moistened grass may act as a dielectric waveguide for ground-based wireless devices and sensors. The results not only provide a working model for predicting path loss for ground-based radio sensors, but suggest a potential method for wireless sensing of bulk moisture content in vegetation.