Performance of Dynamic and Ambiguity-fixed GNSS-derived LEO Orbits in SLR Validation and Network Calibration

For Low Earth Orbiters (LEOs), Satellite Laser Ranging (SLR) is a tool widely applied for the independent and external validation of orbit solutions derived from Global Navigation Satellite System (GNSS) or other radiometric measurements. For various satellite missions over the last decade SLR residuals, i.e., differences between observed and computed ranges, have been at the 1-3 cm RMS level when selecting only measurements from high-performing SLR stations. Refining orbit or observation modeling techniques, e.g., by making use of advanced non-gravitational force modeling or single-receiver ambiguity resolution, allows on the one hand to further reduce SLR residuals. On the other hand, up-to-date orbit solutions reach such a high accuracy and precision that in fact uncertainties in SLR station coordinates and/or range biases start to constitute limiting factors for the achieved levels of SLR residuals.

Especially for LEOs, SLR measurements are not only sensitive to radial, but also to lateral directions. Because different error sources induce different systematic patterns in SLR residuals, the analysis of the latter allows for the estimation of offset corrections for orbits, or, if high-quality orbits are introduced for the SLR residual computation, for the estimation of station coordinate and range bias corrections for the stations in a least-squares adjustment.

We show the performance of reduced-dynamic and kinematic orbit solutions for the gravity mission GRACE-Follow On, as well as the ESA Sentinel and Swarm missions, using state-of-the-art non-gravitational force modeling and undifferenced ambiguity resolution techniques. Ambiguity resolution is enabled by using the high-quality phase bias products and high-rate ambiguity fixed GNSS clock corrections of the Center for Orbit Determination in Europe (CODE). Both the reduction of SLR residuals, and the better separability of orbit and station errors is demonstrated when using these orbits.