Abstract
Below the altitude of peak density height (hmF2), it is relatively easy to obtain the bottomside of the vertical electron density (Ne(h)) profile using measurements from ground-based ionosonde and other sounding instruments. However, accurate modeling of the topside of the Ne(h) profile has always been a challenge. Since the introduction of the radio occultation (RO) technique for ionospheric monitoring, our understanding of the topside ionosphere has significantly improved. This study shows that by assimilating ionosonde foF2 and collocated RO Ne(h) profile data, a full-scale Ne(h) profile at any ionosonde location can be accurately modeled using NeQuick2 electron density model with multiple effective ionization level (Az) parameters. To implement the technique, NeQuick2 was modified with multiple effective parameters with each one of them having a task to model a specific part of the Ne(h) profile separately and exclusively. As a result, the shape of the resulting Ne(h) profile is matched closely with the corresponding experimental RO Ne(h) profile. To assess the accuracy of the technique, we present a comparison of vertical total electron content (VTEC) calculated from experimental (RO retrieved), and NeQuick2 model-assimilated Ne(h) profiles. A very strong correlation has been found between the modeled and experimental Ne(h) profiles based on VTEC values. The experimental and modeled profile TEC values are found to be 99.5% correlated. The proposed assimilation technique is self-sustaining, robust and is not affected by solar activity, season, and geographical location of the ionosonde.
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Data Availability
The radio occultation data used in this research have been obtained from COSMIC-2 constellation database at https://data.cosmic.ucar.edu/gnss-ro/cosmic2/. The scaled data of Sharjah ionosonde have been obtained from SWI Lab (2021) and are available freely at Harvard Dataverse at https://doi.org/10.7910/DVN/UDJJWI.
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Acknowledgements
The author would like to thank COSMIC program team for making COSMIC-2 GPS radio occultation data freely available for scientific purposes. The author is grateful to the Telecommunication/Information, Communication and Technology for Development (T/ICT4D) laboratory of the Abdus Salam International Center for Theoretical Physics (ICTP) for distributing NeQuick2 Fortran code freely for scientific purposes.
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Shaikh, M.M. Retrieval of Ne(h) profile for ionosonde by assimilating collocated radio occultation data into NeQuick2. GPS Solut 25, 145 (2021). https://doi.org/10.1007/s10291-021-01180-5
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DOI: https://doi.org/10.1007/s10291-021-01180-5