Enhanced Measurements of GPS Transmissivity through a Light Rain Event

Abstract

Received Global Positioning System (GPS) signals through a light rain event are measured for 8 GPS satellites. The incident GPS signals are at 1.57542 GHz with right-hand circular polarization (RHCP). The power transmission of GPS signals to the receiver is referred to as GPS Transmissivity (GPS-T). Using 8 GPS orbital tracks improves the spatial and temporal resolution of the GPS-T measurements through the light rain event compared to using only 1 GPS orbital track. In this analysis, the normalized antenna elevation gain pattern is included. However, the normalized antenna azimuth gain pattern is not included because it is assumed to be approximately constant. The relative received powers through the light rain are measured with an antenna that is covered by a fiberglass hemispherical radome. The water-layer’s power transmission loss on the radome (0.05 dB) is neglected because it is much less than the minimum measured power transmission losses during the light rain (∼0.5 dB). Furthermore, the radome’s power transmission loss is eliminated by subtracting the received power during the light rain from the received power when the radome surface is dry during the mostly clear skies overhead. The measured power transmission losses and transmissivities (power transmissions) through the light rain for 8 GPS satellites are shown in 16 plots. In addition, the temporal and spatial variability of these measurements are shown in 2 animations. The impact of these results on GPS operational applications during rain and on potentially detecting ice crystals is discussed.