The ANU GRACE software, developed in the Environmental Geodesy group at the Research School of Earth Sciences, is a suite of programs and scripts that processes the Level-1B data from the GRACE and GRACE Follow-On missions to estimate temporal variations in mass distribution on and within Earth. The analysis process involves integrating satellite orbits then estimating changes in mass on mass concentration elements (known as "mascons") to provide a best-fitting set of parameters to match the observations of position, velocity and range acceleration between the two satellites.

What's different about the ANU space gravity solutions?

There are two fundamental differences in our analysis approach that make our solutions unique:

Range acceleration

We use the time derivative of the range rate observations as the principal inter-satellite observation in our analysis. The use of the range acceleration enhances the spatial localisation of the mass change signals (Allgeyer et al., 2022).

Irregularly shaped mascons

Rather than estimating spherical harmonic coefficients to represent the temporal gravity field, we estimate directly the changes in mass - expressed as a height of equivalent water - on each mascon. We use 12755 primary mascons, each comprised of ~100 smaller ternary mascons. Each ternary mascon is roughly 18x18 km and we add them together to form the primary mascons (Tregoning et al., 2022).

The deliberate ad hoc approach to constructing our primary mascons means that we can form irregularly shaped primary mascons, which means that boundaries of the primary mascons can follow coastlines and/or drainage boundaries. This helps to reduce the leakage of signals across ocean/continent boundaries as well as across drainage basins (McGirr et al., 2023).