On the use of ground and space based GPS measurements in the electron density assimilative model (EDAM)

Ground based measurements of slant total electron content (TEC) can be assimilated into ionospheric models to produce 3D representations of ionospheric electron density. The Electron Density Assimilative Model (EDAM) has been developed for this purpose. Previous tests using EDAM and ground based data have demonstrated that the information on the vertical structure of the ionosphere is limited in this type of data. The launch of the COSMIC satellite constellation provides the opportunity to use radio occultation data which has more vertical information. EDAM assimilations have been run for October 2007. For each run, three data sets have been ingested - only ground based data, only COSMIC data and both ground based and COSMIC data. The results show that both ground and space based data are capable of improving the modelling of the F2 region critical frequency (foF2). The best results are obtained when both data types are assimilated. A comparison between EDAM vertical profiles and those produced using an Abel Transform of the radio occultation data indicates that the representation of the vertical structure if the ionosphere can be improved using ground based data alone. However, degraded results (i.e. worse than the background model) below approximately 200 km must be investigated.