Performance of the improved Abel transform to estimate electron density profiles from GPS occultation data
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The Abel inversion is a straightforward tool to retrieve high-resolution vertical profiles of electron density from GPS radio occultations gathered by low earth orbiters (LEO). Nevertheless, the classical approach of this technique is limited by the assumption that the electron density in the vicinity of the occultation depends only on height (i.e., spherical symmetry), which is not realistic particularly in low-latitude regions or during ionospheric storms. Moreover, with the advent of recent satellite missions with orbits placed around 400 km (such as CHAMP satellite), an additional issue has to be dealt with: the treatment of the electron content above the satellite orbits. This paper extends the performance study of a method, proposed by the authors in previous works, which tackles both problems using an assumption of electron-density separability between the vertical total electron content and a shape function. This allows introducing horizontal information into the classic Abel inversion. Moreover, using both positive and negative elevation data makes it feasible to take into account the electron content above the LEO as well. Different data sets involving different periods of the solar cycle, periods of the day and satellites are studied in this work, confirming the benefits of this improved Abel transform approach.
KeywordsShape Function Electron Content Radio Occultation Slab Thickness Vertical Total Electron Content
We acknowledge to UCAR in Colorado, ISDC in GeoForschungsZentrum and Prof. Victor Rios of the Universidad de Tucuman, Argentina, for the GPSMET, CHAMP and SAC-C data, respectively. Data from Taiwan ionosonde was provided by Prof. Yuei-An Liou of the Center for Space and Remote Sensing Research Institute, Taiwan. The global TEC maps have been retrieved from the International GPS Service. Ionosonde parameters have been extracted from SPIDR web server. This work has been partially supported by “Generalitat de Catalunya” with scholarship 2000FI-00395 and projects TIC-2000-0104-P4-03 and TIC-2001-2356-C02-02.
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