GPS Transmissivity through Light Rain

The Global Positioning System (GPS) is designed to operate in all weather conditions. Here, we discuss a case that involves received GPS signals through a light rain event, with incident energy at 1.57542 GHz right-hand circularly polarized. The power transmission of GPS signals to the receiver is referred to as GPS Transmissivity (GPS-T). The relative received powers through the light rain are measured with an antenna that is covered by a fiberglass hemispherical radome. The average rain rate is measured by a tipping-bucket-type rain gauge. This in situ measurement is used for calculating the approximate uniform water-layer thickness formed on the radome. The power transmission losses through the radome and water-layer thickness combination, the radome thickness alone, and the water-layer thickness alone are computed from conventional theory. The radome’s power transmission loss is eliminated by subtracting the received power during the light rain from the received maximum power during the mostly clear skies. The measured maximum power transmission loss by the light rain for GPS satellite PRN 29 is approximately 2.5 decibels (dB). This translates to a minimum transmissivity of approximately 58%. The impact of these results is discussed.