Penumbra effects on orbital motion of GNSS satellites and their impact on climate investigations

The tremendous improvement of the gravity field models which we are achieving with the last recovering Earths satellite missions like, CHAMP, GRACE and GOCE devoted to its recovery could make feasibile the use of precise orbit determination (POD) of Earth satellites as a tool for sensing a global changes of some key atmosphere parameters like refractivity and extinction. Such improvements indeed, coupled with the huge number of running Earths satellites and combinations of their orbital parameters (namely the nodes) in a gravity field free fashion (GF-free) can magnify the solar radiation pressure acting on MEO satellites ( GPS, Etalon and, in near real future GALILEO) and its smooth modulation through the Earths atmosphere (penumbra). We would remind that The GF-free technique is able to cancel out with n satellite orbital parameters the first n-1 even zonal harmonics of the gravity field. Previously it was demonstrated that the signal we want to detect could in principle emerge from the noise threshold but, , more refined models of the atmosphere would be needed to perform a more subtle analysis. So we will recompute the signal features of penumbra by applying more refined atmospheric models. Finally it is proposed to modify the orbital injection of at least one GALILEO satellite just to magnify penumbra effects on it