Improving the Abel transform inversion using bending angles from FORMOSAT-3/COSMIC
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The FORMOSAT-3/COSMIC satellite constellation has become an important tool toward providing global remote sensing data for sounding of the atmosphere of the earth and the ionosphere in particular. In this study, the electron density profiles are derived using the Abel transform inversion. Some drawbacks of this transform in LEO GPS sounding can be overcome by considering the separability concept: horizontal gradients of vertical total electron content (VTEC) information are incorporated by the inversion method, providing more accurate electron density determinations. The novelty presented in this paper with respect to previous works is the use of the phase change between the GPS transmitter and the LEO receiver as the main observable instead of the ionospheric combination of carrier phase observables for the implementation of separability in the inversion process. Some of the characteristics of the method when applied to the excess phase are discussed. The results obtained show the equivalence of both approaches but the method exposed in this work has the potentiality to be applied to the neutral atmosphere. Recent FORMOSAT-3/COSMIC data have been processed with both the classical Abel inversion and the separability approach and evaluated versus colocated ionosonde data.
KeywordsGPS radio occultation Ionosphere Electron density Abel transform Separability FORMOSAT-3/COSMIC
The authors would like to express their gratitude to the University Corporation for Atmospheric Research (UCAR), the National Space Organization (NSPO) in Taiwan for the availability of FORMOSAT-3/COSMIC constellation data, the International GNSS Service (IGS) for making available IONEX files, the source of ionosonde data SPIDR and, Dr. David Altadill at Ebro Observatory for providing calibrated AS00Q ionosonde data. This work has been partially supported by the Spanish Ministry of Science and Technology and the European Social Funds under the program “Personal Técnico de Apoyo”, and the IBER-WARTK project ESP2007-62676.
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