Global Ocean Mass Change Estimation Using Low-Degree Gravity Field From Satellite Laser Ranging

Satellite laser ranging (SLR) is a well-established geodetic technique for measuring the low-degree time-variable gravity field for decades. However, its application in mass change estimation is limited by low spatial resolution, even for global mean ocean mass (GMOM) change which represents one of the largest spatial scales. After successfully correcting for signal leakage, for the first time, we can infer realistic GMOM changes using SLR-derived gravity fields up to only degree and order 5. Our leakage-corrected SLR GMOM estimates are compared with those from the Gravity Recovery and Climate Experiment (GRACE) for the period 2005 to 2015. Our results show that the GMOM rate estimates from SLR are in remarkable agreement with those from GRACE, at 2.23 versus 2.28 mm/year, respectively. This proof-of-concept study opens the possibility of directly quantifying GMOM change using SLR data prior to the GRACE era. The global mean ocean mass (GMOM) is a significant contributor to the current rise of global sea level. Satellite laser ranging (SLR) has been a proven geodetic technique that can determine low-degree time-varying gravity fields for over three decades. It is possible to derive the GMOM using only long-wavelength gravity field information from SLR because of its global nature. However, the coarse resolution of SLR gravity field makes it unable to differentiate between mass changes from land and oceans. A large portion of land signals leak into the adjacent oceans, leading to significantly underestimated GMOM change rates. To solve this problem, we incorporate geographic knowledge of ocean and land boundaries into the GMOM estimation process. This can help restore the lost land signals and results in an improved GMOM estimate. We compare the SLR estimates with the more reliable results from GRACE, which shows that the GMOM rate from SLR, after correcting for leakage, agrees remarkably well with that from GRACE. This result is encouraging because it allows for the direct quantification of GMOM change for years before 2002, which is critical for understanding long-term global sea level rise. Direct use of satellite laser ranging (SLR)-derived low-degree gravity field yields significantly underestimated global ocean mass rate due to severe signal leakage The leakage-corrected SLR gravity field provides a realistic estimate of global ocean mass rate that agrees remarkably well with Gravity Recovery and Climate Experiment Forward modeling is more effective than the buffer zone technique in leakage correction for low-degree gravity field