# Effects of Equatorial Plasma Bubbles on Multi-GNSS Signals: A Case Study over South China
## 5 Conclusions  
In this work, all-sky airglow images over South China are used to visually determine the EPB structure and depletion degree, and GNSS measurements are used to characterize the corresponding signal quality effects. We systematically analyze the effects of a single EPB event on navigation constellations, including the multi-frequency signals of GPS, Galileo, GLONASS, and BDS. The results are summarized as follows:  
1. The joint airglow-GNSS observations reveal that the center part of the airglow depletion often corresponds to stronger GNSS scintillation, while the edge part of the bubble, which is considered to have the largest density gradient, corresponds to relatively smaller scintillation instead. The sharp fluctuations in dVTEC also correspond to the center of the airglow depletion.
2. EPBs have significant impacts on GNSS signals, including signal strength degradation, loss of lock, and cycle slip, and these impacts are dependent on signal modulation for different GNSS constellations. The overall stability of the L1 band is better than that of the L2 and L5 bands, and signal tracking stability of Galileo is better than that of the others. For frequency selection in dual-frequency positioning, L1C and L2L for GPS, L1C and L5Q for Galileo, L1P and L2C for GLONASS, and L1P and L5P for BDS exhibit great signal tracking stability and could be better combinations during EPB events.
3. The BDS signals are further assessed according to different generations and satellite orbits. The signal tracking of BDS-3 is more stable than that of BDS-2. The performance of the IGSO satellites in BDS is far worse than that of the MEO and GEO satellites, which is likely related to the special signal path trajectory of the IGSO satellite.  
Figure 8: Occurrence rate of error epochs for BDS-2 and BDS-3 and for different orbit types (MEO, GEO, IGSO). This figure is similar to Figure 7.  
**Author Contributions:** Conceptualization, H.H., J.Z., Y.H. and X.W.; methodology, [PERSON], N.W. and X.W.; software, [PERSON], J.C., X.S., K.W. and Q.L.; validation, J.Z., Y.H., N.W., X.W. and F.H.; formal analysis, H.H., Y.T., Z.O. and W.D.; investigation, J.Z., Y.H., and N.W.; resources, [PERSON], J.Z., Y.H., and X.W.; data curation, J.Z., Q.L., F.H. and X.S.; writing--original draft preparation, [PERSON] and J.Z.; writing--review and editing, [PERSON], Y.H., X.W. and F.H.; visualization, [PERSON], J.Z. and [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON] and [PERSON]; funding acquisition, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the National Natural Science Foundation of China (42374181, 42374186, 42274195, 42004136, 42104169, 42104147, 41804150), the Project of Stable Support for Youth Team in Basic Research Field, CAS (YSBR-018), Guangdong Basic and Applied Basic Research Foundation (2021A1515011216, 2022A1515011580, 2020A1515110242), Joint Open Fund of Mengcheng National Geophysical Observatory (MENGO-202217), the USTC Research Funds of the Double First-Class Initiative (YD2080002013), the Opening Funding of Chinese Academy of Sciences dedicated for the Chinese Meridian Project.  
**Data Availability Statement:** The GNSS and airglow data used and/or analyzed during the current study are openly available in [[https://zenodo.org/records/10960624](https://zenodo.org/records/10960624)]([https://zenodo.org/records/10960624](https://zenodo.org/records/10960624)) (doi: 10.5281/zenodo.10960623).  
**Acknowledgments:** We thank NASA/Goddard Space Flight Center for providing the F107 index.  
**Conflicts of Interest:** The authors declare no conflicts of interest.