J 4 , 9 A Generalized Inversion Scheme Inside or for GPS

Radio occultation measurements using the Global Positioning System (GPS) and a receiver in low-Earth orbit (LEO) have recently been shown to provide accurate profiles of atmospheric refractivity, pressure, water vapor and temperature with high vertical resolution [e.g. Kursinski et al., 1996]. When a GPS transmitter and receiver pair are on opposite sides of the atmosphere, the radio signal propagating in the intervening medium is bent due to the atmospheric refractivity gradient. The bending creates a Doppler frequency shift in the received signal and can therefore be obtained directly from the GPS observable. Assuming a spherically symmetric atmosphere, the bending can be expressed as a function of refractivity by an integral equation. When the receiver is located outside the atmosphere, this equation can be inverted via an Abelian integral transformation to generate vertical profiles of refractivity, from which temperature, pressure and water vapor can be derived.