COM-TG: Combined mascon solution

Here we describe how a new mass concentration (mascon) product, COM-TG, is derived from a combination of four separate mascon solutions (GSFC, CSR, ANU, JPL). The combined product has the large-scale accuracy of the JPL solution and the high spatial patterns of the smaller solutions.

What are mascons ?

Mass concentration elements (mascons) are "tiles" used to cover the surface of the Earth on which changes in mass are estimated using data from the GRACE and GRACE Follow-On satellite missions. There are a number of different mascon solutions available globally, all of which have been produced making different assumptions:

the size and shape of the mascons used
defining which mascons are land and which are ocean
how floating ice shelves are handled in polar regions
strategies for adding numerical stability to the data inversions

Consequently, combining mascon solutions turns out to be a rather complex process, but it is possible!

Why a combined mascon solution?

The COM-TG combined mascon solution exploits the benefits of the larger, less correlated mascons of the JPL solution with the higher spatial resolution of the ANU, CSR and GSFC mascon solutions. The resulting product, evaluated on ~100 km mascons, provides estimates of the temporal gravity field that has a RMSE of 3-5 cm with respect to each of the input mascon solutions and produces the expected spatial patterns while removing certain anomalies/idiosyncracies of each of the solutions. The COM-TG solution suppresses noise relative to individual input mascon products and preserves large-scale patterns while maintaining meaningful spatial variability.

The land/ocean coastline boundaries were unified across the input mascon solutions then the Coastline Resolution Improvement (CRI) filter of Wiese et al. (2016) was applied to resolve smearing of signals across coastline boundaries. We assess the sensitivity of the COM-TG solution to the weighting of the input mascon solutions and demonstrate that the results are relatively insensitive to the choice of observation weights.

We also provide a 0.25^o global land-ocean-grounded ice mask to facilitate more straightforward combination of future mascon solutions if adopted by the GRACE processing community.

Publication

Please cite the following if using the COM-TG mascon solution:

McGirr, R. and P. Tregoning, A combined mascon product from multiple analyses of GRACE and GRACE Follow-On space gravity data, Geophysical Research Letters, submitted May 2026.

Fused mascon solution mean (2003-2023) at 1-degree spatial resolution

Files

COM-TG mascon solution

The COM-TG combined mascon solution is provided in netcdf format on a 0.25^o global grid ( COM-TG_200204-202511_all-corrections.nc ). This file also includes the coastline mask (on a 0.25^o grid) used to unify the input mascon solutions.