Monitoring the Marine Atmospheric Refractivity Profiles by Ground-Based GPS Occultation

GPS radio occultation has proved to be a powerful tool for remotely sensing the Earth´s neutral atmosphere and ionosphere. In this letter, we propose a novel approach to retrieving marine tropospheric profiles based on single ground-based GPS occultation observations. A new retrieval method uses the data from a ground-based receiver while the GPS satellites rise or set at the local horizon in the direction of the ocean. The GPS L1 amplitude signals with negative elevation angles are used to retrieve the atmospheric refractivity by artificial neutral networks. The subsequent experiment was carried out on the coast of the Yellow Sea from August 2010 to July 2011. It is shown that the inversion profiles are very consistent with the radiosonde observations. The new method outperforms the Hopfield model, particularly at 0.5-5-km altitude. These results validate the feasibility of retrieving the lower marine atmospheric refractivity from GPS data collected by a single ground-based receiver near the sea surface.