Characterizing Ionospheric Scintillation for Future GNSS Radio Occultation Missions

M. Najmafshar, S. Skone and F. Ghafoori

Peer Reviewed

Abstract:	Multi-frequency multi-constellation approaches exploiting modernized signals are planned for near future radio occultation (RO) missions (e.g., COSMIC-II). Thus it is desirable to employ the most optimal combinations of robust observations for more accurate RO retrievals. Some missions have proposed the use of only L1 (e.g. GPS L1CA and Galileo E1) and L5 (GPS L5 and Galileo E5) for efficiency. Yet recent studies have shown L5 may be susceptible to external sources of interference which compromise signal quality and availability. Given the major investments required to conduct RO missions and the limited amount or even complete lack of L2C, L5, E1, E5 etc. data from operational missions, it is crucial to investigate the ionospheric scintillation impact on RO receiver designs and consider mitigation methods – such as real-time scintillation monitoring, observation weighting schemes, and/or robust tracking schemes. Real RO data from e-POP GAP shows significant degradation in receiver performance during ionospheric scintillations. The effects are more on tracking L2P(Y), where they may cause complete loss of signal for several minutes. In this study we present strategies for characterizing ionospheric scintillation impact on GNSS signals for RO receivers. These measures of scintillation can be used as feedback within the receiver to switch between signal tracking modes and estimate weighting of observations in optimal linear combinations for the atmospheric retrievals. We compare various methods for scintillation characterization on new frequencies for space-based RO observations. Our analysis includes scintillation severity measurement, signal detrending methods, and independent vs. aiding tracking mode comparison. Our results confirm the dependence of scintillation measurements on signal detrending method. Among different methods introduced in this study, wavelet filtering shows good agreement with theoretical values. Also we show RO L2C signal is affected more by ionospheric scintillation and in severe conditions the receiver tracking loop is unable to remain locked on this signal. However by applying L1-aiding strategy, receiver performance increases significantly in its ability to acquire and track L2C signal.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3808 - 3818
Cite this article:	Najmafshar, M., Skone, S., Ghafoori, F., "Characterizing Ionospheric Scintillation for Future GNSS Radio Occultation Missions," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3808-3818.
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