Multi-Instrument Data Analysis System (MIDAS) Imaging of the Ionosphere

Abstract : A new technique has been developed to reveal the temporal and spatial distribution of ionization in the ionosphere and plasmasphere. The technique uses freely-available GPS satellite data over the continents of the Northern Hemisphere to produce fully four-dimensional movies of the ionization distribution. In this report a quantitative, large-scale study has been undertaken to evaluate the technique over the USA. The research focuses on two periods. The first is a geomagnetically quiet time just past solar minimum during February 1997. The second is during current solar maximum around the extreme ionospheric storm of July 2000. Two different types of imaging have been assessed firstly with just ground-based GPS data and then with radio occultation (GPS-to-LEO satellite) data in the inversion. Imaging with ground-based GPS data alone can provide limited but useful information about the vertical profiles of ionization and this is demonstrated during the July 2000 storm. Comparisons with ionosonde observations indicate that GPS/MET radio occultation data improve the determination of the peak electron concentration by providing more information about the vertical profile of ionization. Such satellite data is particularly important in improving the image quality at the edge of the ground-based coverage, over the oceans. Recommendations are made for future research to evaluate the benefit of including data from ionosondes and Langmuir probes into the inversion.