GNSS probing of the ionosphere

It is well recognized that the space weather induces severe ionosphere perturbations capable of causing various technical problems. Therefore, ionosphere monitoring is necessary to obtain real time information for correcting and/or mitigating ionospheric propagation errors in transionospheric radio systems used in telecommunication, navigation and remote sensing. Dual frequency GPS measurements can effectively provide integral information on the electron density along the ray path by computing differential phases of code and carrier phase measurements. Neglecting higher order terms in the refractive index, the differential phase is proportional to the integral of the electron density along the ray path (total electron content - TEC) between the transmitting GNSS satellite and the receiver. Considering the increasing availability of dense GPS networks and the fact that one receiver may track up to more 10 satellites simultaneously, a large number of measurements can be obtained by ground based measurements. In addition to the ground based GPS measurements also measurements onboard Low Earth Orbiting (LEO) satellites may essentially contribute to detect and monitor space weather effects in the Geo-plasma. Thus GPS radio occultation measurements onboard a LEO satellite may provide up to about 200 vertical electron density profiles per day. Topside tracking data for satellite positioning can effectively be used to monitor the 3D electron density distribution of the topside ionosphere/plasmasphere near the orbit plane