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Atmos. Meas. Tech., 11, 2427-2440, 2018
https://doi.org/10.5194/amt-11-2427-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
26 Apr 2018
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 Zhang5,6, Robert Norman5, Marc Schwaerz2,3, Weihua Bai1,3,4, Qifei Du1,3, and Ying Li7 1Beijing Key Laboratory of Space Environment Exploration, National Space Science Center, Chinese Academy of Sciences (NSSC/CAS), 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 Academy of Sciences, Beijing, China
5SPACE Research Centre, RMIT University, Melbourne, VIC, Australia
6School of Environment of Science and Spatial Informatics, China University of Mining and Technology, Xuzhou, China
7Institute of Geodesy and Geophysics (IGG), Chinese 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 higher-order residual ionospheric error (RIE) can still be significant, so it needs to be further mitigated for high-accuracy applications, especially from 35 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-ray-path 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 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 the 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., 11, 2427-2440, https://doi.org/10.5194/amt-11-2427-2018, 2018.
Publications Copernicus
Short summary
In this study, we focused on investigating the causes of the higher-order residual ionospheric error (RIE) in the GNSS RO events, by employing detailed along-ray-path 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.
In this study, we focused on investigating the causes of the higher-order residual ionospheric...
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