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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2017-242
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
31 Aug 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Analysis of ionospheric structure influences on residual ionospheric errors in GNSS radio occultation bending angles based on ray tracing simulations
Congliang Liu1,3, Gottfried Kirchengast2,3,1,5, Yueqiang Sun1,3,4, Kefei Zhang5, Robert Norman5, Marc Schwaerz2,3, Weihua Bai1,3,4, Qifei Du1,3, and Ying Li6 1National Space Science Center, Chinese Academy of Sciences (NSSC/CAS) and Beijing Key Laboratory of Space Environment Exploration, Beijing, China
2Wegener Center for Climate and Global Change (WEGC ) and Institute for Geophysics, Astrophysics, and Meteorology/Institute of Physics, University of Graz, Graz, Austria
3Joint Laboratory on Occultations for Atmosphere and Climate (JLOAC) of NSSC/CAS, Beijing, China, and University of Graz, Graz , Austria
4University of Chinese Acade my of Sciences, Beijing, China
5SPACE Research Centre, RMIT University, Melbourne, VIC, Australia
6Institute of Geodesy and Geophysics (IGG), Chin ese Academy of Sciences, Wuhan, China
Abstract. The Global Navigation Satellite System (GNSS) radio occultation (RO) technique is widely used to observe the atmosphere for applications such as numerical weather prediction and global climate monitoring. The ionosphere is a major error source to RO at upper stratospheric altitudes and a linear dual-frequency bending angle correction is commonly used to remove the first-order ionospheric effect. However, the residual higher-order ionospheric error (RIE) can still be significant so that it needs to be further mitigated for high accuracy applications, especially from 30 km altitude upward where the RIE is most relevant compared to the decreasing magnitude of the atmospheric bending angle. In a previous study we quantified RIEs using an ensemble of about 700 quasi-realistic end-to-end simulated RO events, finding typical RIEs at the 0.1 to 0.5 μrad noise level, but were left with 26 exceptional events with anomalous RIEs at the 1 to 10 μrad level that remained unexplained. In this study, we focused on investigating the causes of the high RIE of these exceptional events, employing detailed along-raypath analyses of atmospheric and ionospheric refractivities, impact parameter changes, and bending angles and RIEs under asymmetric and symmetric ionospheric structures. We found that the main causes of the high RIEs are a combination of physics-based effects, where asymmetric ionospheric conditions play the primary role, more than the ionization level driven by solar activity, and technical ray tracer effects due to occasions of imperfect smoothness in ionospheric refractivity model derivatives. We also found that along-ray impact parameter variations of more than 10 to 20 m are well possible due to ionospheric asymmetries, and depending on prevailing horizontal refractivity gradients are positive or negative relative to the initial impact parameter at the GNSS transmitter. Furthermore, mesospheric RIEs are found generally higher than upper stratospheric ones, likely due to being closer in tangent point heights to the ionospheric E layer peaking near 105 km, which increases RIE vulnerability. In future we will further improve the along-ray modeling system to fully isolate technical from physics-based effects and to use it beyond this work for additional GNSS RO signal propagation studies.

Citation: Liu, C., Kirchengast, G., Sun, Y., Zhang, K., Norman, R., Schwaerz, M., Bai, W., Du, Q., and Li, Y.: Analysis of ionospheric structure influences on residual ionospheric errors in GNSS radio occultation bending angles based on ray tracing simulations, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-242, in review, 2017.
Congliang Liu et al.
Congliang Liu et al.
Congliang Liu et al.

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