Retrieval of atmospheric refractivity profiles from ground-based GPS measurements

An alternative remote sensing technique for the retrieval of atmospheric refractive index profiles is presented. It is an optimization procedure for the inversion of ground-based GPS phase measurements collected at low elevation angles. The Abel inversion, usually adopted to infer atmospheric profiles from space-based radio occultation observations, cannot be applied to the inversion of ground-based measurements. Therefore, we propose a technique which iteratively looks for the refractive index profile by minimizing a cost function. This function depends on several measurements of signal times-of-flight, provided that the correspondent real signal arrival angles could be known with sufficient accuracy. Although different optimization procedures could be used, a non-linear least squares procedure has been adopted in this first attempt. Starting from a different first guess profile, the retrieved refractivity profile is in good agreement with the reference one, which is used to derive the observables.