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Article

New Higher-Order Correction of GNSS RO Bending Angles Accounting for Ionospheric Asymmetry: Evaluation of Performance and Added Value

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National Space Science Center, Chinese Academy of Sciences (NSSC/CAS) and Beijing Key Laboratory of Space Environment Exploration, 100190 Beijing, China
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Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, 8010 Graz, Austria
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Joint Laboratory on Occultations for Atmosphere and Climate (JLOAC) of NSSC/CAS, 100190 Beijing, China, and University of Graz, 8010 Graz, Austria
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Danish Meteorological Institute (DMI), 2100 Copenhagen, Denmark
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(21), 3637; https://doi.org/10.3390/rs12213637
Received: 10 September 2020 / Revised: 22 October 2020 / Accepted: 28 October 2020 / Published: 5 November 2020
The residual ionospheric error (RIE) from higher-order terms in the refractive index is not negligible when using global navigation satellite system (GNSS) radio occultation (RO) data for climate and meteorology applications in the stratosphere. In this study, a new higher-order bending angle RIE correction named “Bi-local correction approach” has been implemented and evaluated, which accounts for the ray path splitting of the dual-frequency GNSS signals, the altitude of the low Earth orbit (LEO) satellite, the ionospheric inbound (GNSS to tangent point) vs. outbound (tangent point to LEO) asymmetry, and the geomagnetic field. Statistical results based on test-day ensembles of RO events show that, over the upper stratosphere and mesosphere, the order of magnitude of the mean total RIE in the bi-local correction approach is 0.01 μrad. Related to this, the so-called electron-density-squared (Ne2) and geomagnetic (BNe) terms appear to be dominant and comparable in magnitude. The BNe term takes negative or positive values, depending on the angle between the geomagnetic field vector and the direction of RO ray paths, while the Ne2 term is generally negative. We evaluated the new approach against the existing “Kappa approach” and the standard linear dual-frequency correction of bending angles and found it to perform well and in many average conditions similar to the simpler Kappa approach. On top of this, the bi-local approach can provide added value for RO missions with low LEO altitudes and for regional-scale applications, where its capacity to account for the ionospheric inbound-outbound asymmetry as well as for the geomagnetic term plays out. View Full-Text
Keywords: GNSS radio occultation; bending angle retrieval; residual ionospheric errors; bi-local correction approach; Kappa correction approach GNSS radio occultation; bending angle retrieval; residual ionospheric errors; bi-local correction approach; Kappa correction approach
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MDPI and ACS Style

Liu, C.; Kirchengast, G.; Syndergaard, S.; Schwaerz, M.; Danzer, J.; Sun, Y. New Higher-Order Correction of GNSS RO Bending Angles Accounting for Ionospheric Asymmetry: Evaluation of Performance and Added Value. Remote Sens. 2020, 12, 3637. https://doi.org/10.3390/rs12213637

AMA Style

Liu C, Kirchengast G, Syndergaard S, Schwaerz M, Danzer J, Sun Y. New Higher-Order Correction of GNSS RO Bending Angles Accounting for Ionospheric Asymmetry: Evaluation of Performance and Added Value. Remote Sensing. 2020; 12(21):3637. https://doi.org/10.3390/rs12213637

Chicago/Turabian Style

Liu, Congliang, Gottfried Kirchengast, Stig Syndergaard, Marc Schwaerz, Julia Danzer, and Yueqiang Sun. 2020. "New Higher-Order Correction of GNSS RO Bending Angles Accounting for Ionospheric Asymmetry: Evaluation of Performance and Added Value" Remote Sensing 12, no. 21: 3637. https://doi.org/10.3390/rs12213637

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