A New Realization of the Terrestrial Reference Frame: Combining GPS, SLR and VLBI at the Observation Level from 2010–2022

We describe the development and assessment of a new terrestrial reference frame (TRF) based on combining GPS, SLR and VLBI at the observation level over the period 2010–2022. Included in the solution, in addition to station coordinates and precise orbit solutions for all participating satellites, are Earth orientation parameters (EOP) and low-degree zonal coefficients (J2 and J3) of the geopotential. The overall solution concept grew from earlier efforts to realize a TRF using GPS data alone, capitalizing on GPS receivers on the ground and in low-Earth orbit (LEO). Here we add observations from both the SLR and VLBI techniques, which provide the foundation for traditional realizations of the TRF.

In linking the GPS and SLR techniques, our approach dispenses with traditional ground survey ties, relying exclusively on space ties from the GRACE and Jason LEO missions. In addition to SLR from these satellites, we include observations from the dedicated LAGEOS satellites, which prove particularly important for recovering low-degree gravity. A major evolution of our approach is the addition of VLBI at the observation level. Lacking a robust tie in Earth orbit for VLBI observations, we apply as constraints the published ground survey ties to nearby GPS stations, enforcing inclusion of the corresponding tracking data in the solutions. The VLBI effort is in the exploratory phase, and further tuning of the strategy is needed to better exploit collocations with both GPS and SLR. About 40% of the participating solution arcs (spanning 2010–2022) now include VLBI and support accurate recovery of UT1 as part of the EOP solution.

Though the resulting TRF solution is based on only 12.6 years of data, it is competitive with ITRF2020 in terms of fundamental frame parameters (origin and scale) and their temporal evolution, both linear and seasonal. The relative rates of origin (3D) and scale (at Earth's surface) are 0.2 mm yr^-1 and 0.1 mm yr^-1 respectively. Absolute scale (at epoch 2015.0) and 3D origin both differ by 2 mm. One advantage of our technique is that precise orbit solutions for both GRACE and Jason missions, defined in the realized TRF, are byproducts of the overall solution. We use the Jason orbit solutions to characterize the impact of contemporary TRF errors on sea level variations (both global and regional) and discuss the implications of these results.