Simulation of a Future SLR Satellite to Improve Low‐Degree Gravity Estimates

Abstract

The Gravity Recovery and Climate Experiment (GRACE; 2002–2017) and GRACE Follow‐On (2018‐present) have observed Earth's monthly mass change with unprecedented spatial resolution. These missions have long relied on satellite laser ranging (SLR) measurements to replace the C2,0 coefficient, which GRACE recovers poorly. Recent work has also shown the need for SLR‐determined C3,0 when GRACE operates with a single accelerometer. However, it was not until the 2012 launch of the Laser Relativity Satellite that the SLR data gained the sensitivity to recover C3,0 accurately. These low‐degree gravity coefficients represent large‐scale mass transport and small changes in their values have implications for ice sheet, ocean mass, and water storage estimates. To fully exploit SLR's utility for time‐variable gravity (TVG), future satellite orbits should be selected to maximize their sensitivity to the gravity field. In this work, we present results from a simulation study of a hypothetical SLR satellite in which we generate 1 year of data to satellites placed across varying inclinations. We also simulate seven current SLR satellites to show realistic improvements from the new satellite. When compared to the known truth input, a low‐inclination satellite (<∼ 45°) most improves the low‐degree gravity terms, especially the even zonals which show a significant decorrelation. From this, we investigate recovery of the annual variability in the simulated signal and find recovery of the sine component improves by up to 41%. This has important implications when considering future SLR satellites in the context of TVG.

Impacts of SLR Ground Station Geographic Distribution on Time‐Variable Gravity Recovery

“…Tucker et al. (2022) simulated the impact of a hypothetical new SLR satellite on TVG estimates. They found that a new low‐inclination SLR satellite, when combined with the current SLR satellite constellation, would significantly decorrelate the even zonals and order 1 terms and lead to greatly improved recovery of these coefficients.…”

“…(2022), real data files are used for the year beginning 6 January 2019 to determine observation numbers and epochs for the current network. Because laser ranging cannot occur through clouds, we use NCEP/DOE Reanalysis II total cloud cover data to approximate tracking probabilities and statistics for hypothetical new stations (Kanamitsu et al., 2002; Tucker et al., 2022). No station‐specific range biases are estimated.…”

“…Our simulation procedure follows from Tucker et al. (2022), who applied established methods for simulating mass‐change recovery to SLR (e.g., Deccia et al., 2022; Loomis et al., 2012; Wiese et al., 2022). The overall workflow will be briefly described here.…”

“…Both the number of ground stations and satellites are constantly evolving, leading to improvements in SLR-derived gravity estimates. Tucker et al (2022) determined TVG improvements from the addition of a hypothetical new satellite. They found that a new SLR satellite, depending on its inclination, decorrelated certain coefficients by up to an order of magnitude, and led to significantly improved signal recovery.…”

A Simulation Study for Future Geodetic Satellites Tracked by Satellite Laser Ranging

“…Accordingly, Trucker et al. (2022) performed simulations to determine the most favorable inclination angle for a future geodetic satellite that would improve the quality of gravity potential coefficient determination, however, other geodetic parameters that can be derived from SLR and the correlations between gravity field coefficients, geocenter motion and ERPs were not discussed by Trucker et al. (2022).…”