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According to general relativity theory (GRT), the geopotential difference(GD) can be determined by comparing the change in time difference betweenprecise clocks using the precise point positioning (PPP) time transfertechnique, referred to as the relativistic PPP time comparison approach. Wefocused on high-precision time comparison between two precise clocks fordetermining the GD using the relativistic PPP time transfer,and conductedsimulation experiments to validate the approach. In the experiments, weconsider three cases to evaluate the performance of the approach using clockswith different stabilities, namely, the frequency stabilities of the clocksequipped at three selected ground stations are respectively (Case 1), (Case 2),and (Case 3) at time period. Conclusions are drawn from the experimentalresults. First, high-precision clocks can significantly improve the accuracyfor 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-BRUXare improved in Cases 2 and 3. The frequency stabilities of Cases 1-3 areapproximately 4.28*10-16, 4.00*10-17, and 3.22*10-17 at 10-day averaging timefor OPMT-BRUX, respectively, and for PTBB-BRUX, these values are approximately3.73*10-16, 8.17*10-17, and 4.64*10-17. Second, the geopotential differencebetween any two stations can be determined at the decimeter level, with itsaccuracy being consistent with the stabilities of the time links in Cases 1-3.In Case 3, the determined geopotential differences between OPMT and BRUXdeviate from the EIGEN-6C4 model values by -0.64 m2/s2 with an uncertainty of1.11 m2/s2, whereas the deviation error between PTBB and BRUX is 0.76 m2/s2with an uncertainty of 1.79 m2/s2. The approach proposed in this study can bealso applied to testing GRT.

Determining geopotential difference via relativistic precise point positioning time comparison: A case study using simulated observations