Combining Radio Occultation Measurements with Other Instruments to Map the Ionospheric Electron Concentration

The Multi-Instrument Data Analysis System (MIDAS) algorithm is a spatial and temporal imaging program for the atmosphere and ionosphere. This analysis algorithm can routinely use dual-frequency ground-based observations from the GPS satellites to produce four-dimensional images of electron concentration over very large geographical regions (potentially globally). MIDAS also has the facility to incorporate other ionospheric measurements, such as electron-density profiles from inverted ionograms or in-situ measurements of ionization concentration from satellites in low-earth-orbit. The main limitation to the spatial resolution in ionospheric tomography is due to the limited geometrical coverage provided by the satellite to ground ray paths. This problem, known as the missing horizontal rays, can be overcome by the data collected by the new radio-occultation satellites. The simultaneous inversion of both satellite-to-ground and satellite-to-satellite GPS data in a single algorithm (MIDAS) provides a greatly improved geometry in comparison to that found when using either data set independently. Experimental results demonstrate the inversion imaging when radio-occultation data are included in the inversion. The potential benefit in using CHAMP data in such as system is discussed.