Geopotential Determination Based on Precise Point Positioning Time Comparison: A Case Study Using Simulated Observation

Abstract

According to general relativity theory (GRT), the geopotential difference (GD) can be determined by comparing the change in time difference between precise clocks using the precise point positioning (PPP) time transfer technique, referred to as the relativistic PPP time comparison approach. We focused on high-precision time comparison between two precise clocks for determining the GD using the relativistic PPP time transfer,and conducted simulation experiments to validate the approach. In the experiments, we consider three cases to evaluate the performance of the approach using clocks with different stabilities, namely, the frequency stabilities of the clocks equipped at three selected ground stations are respectively (Case 1), (Case 2), and (Case 3) at time period . Conclusions are drawn from the experimental results. First, high-precision clocks can significantly improve the accuracy for PPP time transfer, but the improvement is limited by measurement noises. Compared to Case 1, the long-term stabilities of OPMT-BRUX as well as PTBB-BRUX are improved in Cases 2 and 3. The frequency stabilities of Cases 1-3 are approximately 4.28 × 10 -16 , 4.00 × 10 -17 , and 3.22 × 10 -17 at 10-day averaging time for OPMT-BRUX, respectively, and for PTBB-BRUX, these values are approximately 3.73 × 10 -16 , 8.17 × 10 -17 , and 4.64 × 10 -17 . Second, the geopotential difference between any two stations can be 13 tdetermined at the decimeter level, with its accuracy being consistent with the stabilities of the time links in Cases 1-3. In Case 3, the determined geopotential differences between OPMT and BRUX deviate from the EIGEN-6C4 model values by -0.64 m 2 /s 2 with an uncertainty of 1.11 m 2 /s 2 , whereas the deviation error between PTBB and BRUX is 0.76 m 2 /s 2 with an uncertainty of 1.79 m 2 /s 2 . The approach prosed in this study can be also applied to testing GRT.

Higher order ionospheric effects in testing gravitational redshift by space frequency signal transfer

“…Due to the increasing requirements for high precision of time and frequency measurements, such as tests of GRS (Shen et al 2017;Sun et al 2021), fundamental quantum physics (Delva et al 2017), gravity potential, orthometric height determination (Cai et al 2020) and redefinition of the second by optical clocks (Riehle 2015), high-precision atomic clocks have developed very quickly, especially in the case of optical atomic clocks (OACs). The stability of atomic clocks had been greatly improved to 7 × 10 −19 (Oelker et al 2019;McGrew et al 2018) and the technique of OACs down-conversion for microwave frequencies has since reached an instability of 10 −18 (Nakamura et al 2020).…”