Ionospheric (H-atom) Tomography: a Feasibility Study using GNSS   Reflections
  In this report we analyze the feasibility of ionospheric monitoring using GNSS technology. The focus will be on the use of LEO GNSS data, exploiting GNSS Reflections, Navigation and Occultation TEC measurements. In order to attack this question, we have simulated GNSS ionospheric TEC data as it would be measured from a polar LEO (exploiting Navigation, Occultation and Reflection TEC data) and IGS ground stations, through the use of a climatic ionospheric model (we have explored both NeQuick and PIM). We have then developed a new tomographic approach inspired on the physics of the hydrogen atom, which has been compared to previous successful but somewhat awkward methods (using a voxel representation) and employed to retrieve the Electronic Density field from the simulated TEC data. These tomographic inversion results using simulated data demonstrate the significant impact of GNSS-R and GNSS-NO data: 3D ionospheric Electron Density fields are retrieved over the oceans quite accurately, even as, in the spirit of this initial study, the simulation and inversion approaches avoided intensive computation and sophisticated algorithmic elements (spatio-temporal smoothing). We conclude that GNSS-R data can contribute significantly to the GIOS (Global/GNSS Ionospheric Observation System). 
Josep Marco, Giulio Ruffini, Leonardo Ruffini