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Session P6: Present and Emerging Applications and Techniques for Time and Frequency using GNSS/RNSS/LEO and Optics

Comparison of GPS Frequency-Transfer Performance between JPL’s GIPSY PPP and BIPM’s IPPP
Daphna G. Enzer and David W. Murphy, Jet Propulsion Laboratory, California Institute of Technology
Location: Beacon A

GPS can be used an effective tool for comparing frequencies across large distances to better than 1E-16 [1]. At the Jet Propulsion Laboratory (JPL) we process GPS receiver data using GIPSY-OASIS (GPS-Inferred Positioning System and Orbit Analysis Simulation Software) which uses wide-lane phase bias ambiguity resolution [2] as part of its PPP (Precise Pointing Positioning) algorithm. To process GPS data for the Deep Space Atomic Clock (DSAC) mission [3], we further devised an algorithm and software for concatenating daily files and correcting for phase jumps and data gaps [4]. Here we compare the frequency-transfer performance of our GIPSY PPP technique, applied to ground receivers, with the well-proven IPPP technique [5] used at the International Bureau of Weights and Measures (BIPM). We process 10 months of Germany to United States link data [6] between two International GNSS Service (IGS) stations, both referenced to stable clocks steered to Universal Coordinated Time (UTC). We then subtract two-way satellite time and frequency transfer (TWSTFT) link data [7] to remove the long-term clock instability component. These same link data were processed with IPPP and reported on by Petit and Meynadier at last year’s PTTI conference [8]. We compare the two techniques and discuss the viability of using GIPSY PPP instead of IPPP [7] for transcontinental frequency transfer.
[1] Gérard Petit, “Sub?10–16 accuracy GNSS frequency transfer with IPPP,” GPS Solutions 25, Article number: 22 (January 2021).
[2] Willy Bertiger, et al., “Single Receiver Phase Ambiguity Resolution with GPS Data,” Journal of Geodesy 84 (March 2010): pp. 327-337.
[3] Eric Burt, et al., “Demonstration of a Trapped-Ion Atomic Clock in Space,” Nature 595 (July 2021): pp. 43-47.
[4] Daphna Enzer, David Murphy and William Diener, “Frequency Comparisons via GPS Carrier-phase: Jump Processing, Temperature Compensation and Zero/Short-baseline Noise-floors,” in Proc. of the 50th Annual PTTI, Reston, VA (January 28-31, 2019): pp. 68-82.
[5] Gérard Petit, et al., “1 × 10?16 Frequency Transfer by GPS PPP with Integer Ambiguity Resolution,” Metrologia 52, no. 2 (April 2015): pp. 301-309.
[6] Data from International GNSS Service, Daily 30-second observation data, Greenbelt, MD, USA:NASA Crustal Dynamics Data Information System (CDDIS), Accessed July 23, 2021, Subset obtained: 2019-12-27 to 2020-10-26 at http://cddis.gsfc.nasa.gov/Data_and_Derived_Products/GNSS/daily_gnss_o.html.
[7] Data used were submitted by laboratories for UTC, and processed by the BIPM.
[8] Gérard Petit and Frédéric Meynadier, “IPPP Links for UTC: Comparison to Existing Techniques,” in Proc. of the 52nd Annual PTTI, virtual conference (January 25–28, 2021): pp. 71-86.



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