SLR Simulations to Improve Time-Variable Gravity: Evaluating the Impact of Combination Solutions and a Future Satellite

The Gravity Recovery and Climate Experiment (GRACE) has been known to poorly recover the low degree zonal coefficients of the gravity field. Towards the end of its life, GRACE operated with only a single accelerometer, which further degraded these coefficients. The recently launched GRACE Follow-On (GRACE-FO) continues to observe Earth’s mass change, providing critical measurements of time-varying geophysical signals. However, one of the GRACE-FO satellites suffers from an underperforming accelerometer and a transplant algorithm is used to map data from the functioning instrument. This has created an additional challenge for estimating the low degree zonal coefficients.

Satellite Laser Ranging (SLR) data have long supplemented GRACE gravity estimates. These passive spherical satellites are covered in reflectors to allow laser ranging measurements from a global network of ground stations. On its own SLR can recover low-degree gravity fields which have been used to support the GRACE estimates. The 2012 launch of the Laser Relativity Satellite (LARES) led to large improvements in SLR’s ability to estimate C3,0. Conventionally, these SLR-derived estimates are substituted directly into the GRACE estimates. This approach neglects the influence of higher order terms due to correlated errors in the SLR solution. In this work we simulate SLR and GRACE data to investigate a combined solution at the normal equation level. Motivated by LARES’s effect on the solution, we also simulate a potential new SLR satellite and search for an optimal orbit to improve the gravity recovery. We present results demonstrating the improvements from a combined SLR and GRACE solution as well as the impact of a hypothetical SLR satellite on gravity field recovery.