NASA - National Aeronautics and Space Administration

Satellite laser ranging (SLR) observations have long been relied upon for measuring changes in Earth's dynamic oblateness, C20 . This major component of Earth's time-variable gravity field is not well observed by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, leading to the common practice of replacing their values with those obtained by SLR. The C30 coefficient, which has a large impact on the recovered Antarctic Ice Sheet mass changes, is shown here to be poorly observed by GRACE/GRACE-FO when either mission is operating without two fully functional accelerometers. The GRACE spacecraft pair operated nominally until October 2016 when one accelerometer was powered off due to battery limitations, while GRACE-FO is currently excluding one accelerometer from the data processing due to elevated noise levels. Beginning with the launch of Laser Relativity Satellite in 2012, SLR-derived C30 values are suitable for replacing any problematic GRACE/GRACE-FO estimates, enabling the accurate recovery of Antarctic Ice Sheet mass changes, among others.