A RAYTRACING INVERSION PROCEDURE FOR THE EXTRACTION OF THE ATMOSPHERIC REFRACTIVITY FROM GNSS TRAVEL-TIME DATA

Abstract

We present an inversion procedure for the extraction of atmospheric parameters from travel-time data of signals emitted by Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS). The procedure uses a tomographic approach, using raytracing to obtain the propagation trajectories of the electromagnetic waves. In order to allow the application of this procedure in systems processing large amounts of data, as in operational weather forecasting, we have paid attention to balance the computing time needed, the robustness of the algorithm and the accuracy of the result. We describe the inversion procedure used to extract the refractivity field. In cases cases where moderate amounts of data are available we have aimed to extract the vertical profile (i.e. we assumed that the refractivity depends only on height). We have compared this procedure with the Abel transform inversion approach, the baseline algorithm currently used for radio occultation observations, which requires the assumption that the observed field is spherically symmetric.