Improvement of GPS/MET ionospheric profiling and validation using the Chung-Li ionosonde measurements and the IRI model

The retrieval processes of ionospheric profiling from radio occultation observations usually assume spherical symmetry of electron density distribution at the locality of occultation and use the Abel integral transform to invert the measured total electron content (TEC) values. In this paper, we have considered the effect of large-scale horizontal gradient and/or inhomogeneous electron density and developed a compensation procedure for measured TEC values through several close-up occultation observations. The compensated TEC values are then used to yield electron densities through the Abel inversion. In order to assess the accuracy of GPS/MET ionospheric electron density retrievals, coincidences of the Chung-Li digisonde data with observed GPS/MET occultations have been examined. From 232 matches during the GPS/MET mission, the rms f₀F₂ differences between the digisonde measurements and the GPS/MET retrievals are improved from 1.58 MHz to 1.41 MHz. Further validation of the improved retrieval processes has also been investigated by means of over thirty-eight thousand simulated occultation observations within a reference GPS/MET experiment using the International Reference Ionosphere (IRI) 2001 model. The results show successful improvement of overestimates (underestimates) on low (high) retrieved f₀F₂.