Abstract
In this study, we determine the near real-time (NRT) clocks of the Global Positioning System (GPS) and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) satellites in the Taiwan RO Process System (TROPS), which is mainly designed for the data processing in both the FORMOSAT-3/COSMIC (F3C) and FORMOSAT-7/COSMIC-2 (F7C2) satellite missions. The accuracy of GNSS clocks defines the quality of the atmospheric excess phase, which is used for the retrieval of bending angle profiles in GNSS radio occultation (RO) observations. The accuracy of the NRT GNSS clocks is assessed by comparing the clock rate, clock stability and clock-induced positioning error on receivers with the final solutions given by the European Space Agency (ESA). Overall, the standard deviations of the clock rates from TROPS agree with those from ESA within 0.05 mm/s over 2304 clock solutions. Additionally, we find that the clock stability of the GPS Block IIF type (3 × 10−13) is an order of magnitude better than that of IIR Block types (3 × 10−12) over a time interval of 30 s. In comparison, the stabilities of GLONASS clocks are approximately 3 × 10−12. We quantify the NRT clock error on the receiver positioning by using the precise point positioning technique obtained from the Bernese GNSS software. The 3-dimensional clock-induced positioning error is approximately 3.3, 3.2 and 0.9 cm for station AUCK and 6.9, 6.3 and 3.1 cm for station NRC1 for the GPS-only, GLONASS-only and GPS + GLONASS cases, respectively. For GNSS-RO applications, the bending angle profiles derived using TROPS GPS clocks agree with the COSMIC Data Analysis and Archive Center products to within 0.01–1.00 μrad. However, this is not the case for the GLONASS clock, because the GLONASS clock-induced errors on the RO profile are 10–100 times greater than those induced by the GPS clock. This suggests that different weightings should be used for RO applications, such as data assimilation, when different satellite clocks are involved in GNSS-RO retrievals. This study serves as a reference for assessing the impact of GNSS clocks on both GNSS-POD (precise orbit determination) and GNSS-RO in preparation for the F7C2 satellite mission.
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References
Allan DW (1987) Time and frequency (time-domain) characterization, estimation, and prediction of precision clock and oscillators. IEEE Trans Ultrason Ferroelectr Freq Control 34(6):647–654
Beyerle G, Schmidt T, Michalak G, Heise S, Wickert J, Reigber C (2005) GPS radio occultation with GRACE: atmospheric profiling utilizing the zero difference technique. Geophys Res Lett. https://doi.org/10.1029/2005GL023109
Cai C, Gao Y (2013) Modeling and assessment of combined GPS/GLONASS precise point positioning. GPS Solut 17(2):223–236. https://doi.org/10.1007/s10291-012-0273-9
Chung YD, Yeh TK, Xu G, Chen CS, Hwang C, Shih HC (2016) GPS height variations affected by ocean tidal loading along the coast of Taiwan. IEEE Sens J. https://doi.org/10.1109/JSEN.2016.2538325
Dach R, Bohm J, Lutz S, Steigenberger P, Beutler G (2010) Evaluation of the impact of atmospheric pressure loading modeling on GNSS data analysis. J Geod 85(2):75–91. https://doi.org/10.1007/s00190-010-0417-z
Dach R, Lutz S, Walser P, Fridez P (2015) Bernese GNSS Software Version 5.2, Astronomical Institute. University of Bern, Switzerland
Estey LH, Meerten CM (1999) TEQC: the multi-purpose toolkit for GPS/GLONASS data. GPS Solut 3(1):42–49
Griggs E, Kursinski E, Akos D (2015) Short-term GNSS satellite clock stability. Radio Sci 50:813–826. https://doi.org/10.1002/2015RS005667
Hauschild A, Montenbruck O, Steigenberger P (2013) Short-term analysis of GNSS clocks. GPS Solut 17(3):295–307. https://doi.org/10.1007/s10291-012-0278-4
Ho S et al (2012) Reproducibility of GPS radio occultation data for climate monitoring: profile-to-profile inter-comparison of CHAMP climate records 2002 to 2008 from six data centers. J Geophys Res 117:D18111. https://doi.org/10.1029/2012JD017665
Hwang C, Tseng TP, Lin T, Švehla D, Schreiner B (2009) Precise orbit determination for the FORMOSAT-3/COSMIC satellite mission using GPS. J Geod 83(5):477–489. https://doi.org/10.1007/s00190-008-0256-3
Hwang C, Tseng TP, Lin TJ, Švehla D, Hugentobler U, Chao BF (2010) Quality assessment of FORMOSAT-3/COSMIC and GRACE GPS observables: analysis of multipath, ionospheric delay and phase residual in orbit determination. GPS Solut 14(1):121–131. https://doi.org/10.1007/s10291-009-0145-0
Li YS, Hwang C, Tseng TP, Huang CY, Bock H (2014) A near real-time, automatic orbit determination system for COSMIC and its follow-on satellite mission: analysis of orbit and clock errors on radio occultation. IEEE Trans Geosci Remote Sens 52(6):3192–3203. https://doi.org/10.1109/TGRS.2013.2271547
Li X, Ge M, Dai X, Ren X, Fritsche M, Wickert J, Schuh H (2015) Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS: BeiDou and Galileo. J Geod 89(6):607–635. https://doi.org/10.1007/s00190-015-0802-8
Montenbruck O, Andres Y, Bock H, van Helleputte T, van den IJssel J, Loiselet M, Marquardt C, Silvestrin P, Visser P, Yoon Y (2008) Tracking and orbit determination performance of the GRAS instrument on Metop-A. GPS Solut 12(4):289–299. https://doi.org/10.1007/s10291-008-0091-2
Montenbruck O, Hauschild A, Andres Y, von Engeln A, Marquardt C (2013) (Near-) real-time orbit determination for GNSS radio occultation processing. GPS Solut 17(2):199–209. https://doi.org/10.1007/s1029-012-027
Petit G, Luzum B (eds) (2010) IERS conventions (2010), IERS technical note 36. Verlag des Bundesamts für Kartographie und Geodäsie, Frankfurt am Main. http://tai.bipm.org/iers/conv2010/
Rebischung P, Griffiths J, Ray J, Schmid R, Collilieux X, Garayt B (2012) IGS08: the IGS realization of ITRF2008. GPS Solut 16(4):483–494. https://doi.org/10.1007/s10291-011-0248-2
Schreiner W, Rocken C, Sokolovskiy S, Hunt D (2010) Quality assessment of COSMIC/FORMOSAT-3 GPS radio occultation data derived from single- and double-difference atmospheric excess phase processing. GPS Solut 14(1):13–22. https://doi.org/10.1007/s10291-009-0132-5
Shi C, Yi W, Song W, Lou Y, Yao Y, Zhang R (2013) GLONASS pseudorange inter-channel biases and their effects on combined GPS/GLONASS precise point positioning. GPS Solut 17(4):439–451. https://doi.org/10.1007/s10291-013-0332-x
Sośnica K, Thaller D, Dach R, Steigenberger P, Beutler G, Arnold D, Jäggi A (2015) Satellite laser ranging to GPS and GLONASS. J Geod 89(7):725–743. https://doi.org/10.1007/s00190-015-0810-8
Tseng TP, Zhang K, Hwang C, Hugentobler U, Wang CS, Choy S, Li YS (2014) Assessing antenna field of view and receiver clocks of COSMIC and GRACE satellites: lesson for COSMIC-2. GPS Solut 18(2):219–230. https://doi.org/10.1007/s10291-013-0323-y
Tseng TP, Hwang C, Sośnica K, Kuo CY, Liu YC, Yeh WH (2017) Geocenter motion estimated from GRACE orbits: the impact of F10.7 solar flux. Adv Space Res. https://doi.org/10.1016/j.asr.2016.02.003
Weber G (2006) Streaming real time IGS data and products using NTRIP. Proc IGS Workshop 2006:105–109
Yeh TK, Hwang C, Huang JF, Chao BF, Chang MH (2011) Vertical displacement due to ocean tidal loading around Taiwan based on GPS observations. Terr Atmos Ocean 22(4):373–382. https://doi.org/10.3319/TAO.2011.01.27.01(T)
Yi W, Song W, Lou Y, Shi C, Yao Y (2016) A method of undifferenced ambiguity resolution for GPS+GLONASS precise point positioning. Sci Rep 6:26334. https://doi.org/10.1038/srep26334
Acknowledgements
This study is funded by projects under grant numbers NSPO-S-102024, NSPO-S-103039, NSPO-S-105049 and NSPO-S-105058. We thank the TACC team in Taiwan CWB for their contributions to the F3C and F7C2 projects. We thank UCAR/COSMIC for providing the CDAAC software for the RO result comparisons. We are also grateful to IGS, CODE and ESA for providing the GNSS-related products. We thank anonymous reviewers for their helpful comments that improved the quality of the paper.
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Tseng, TP., Chen, SY., Chen, KL. et al. Determination of near real-time GNSS satellite clocks for the FORMOSAT-7/COSMIC-2 satellite mission. GPS Solut 22, 47 (2018). https://doi.org/10.1007/s10291-018-0714-1
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DOI: https://doi.org/10.1007/s10291-018-0714-1