ANU GRACE Data Analysis: Characteristics and Benefits of Using Irregularly Shaped Mascons

Abstract

The Gravity Recovery and Climate Experiment (GRACE) space gravity mission was one of the most successful space geodesy missions operating for 12 years beyond the planned mission length and impacting a vast array of science disciplines including hydrology, oceanography, crustal deformation, and earthquake seismology. Temporal gravity field solutions have been provided as Level-2 data products from a number of different processing centers (e.g.,

ANU GRACE Data Analysis: Orbit Modeling, Regularization and Inter‐satellite Range Acceleration Observations

“…Differences between the three analysis approaches mean that one should not necessarily expect to find exact agreement between the solutions. The most significant differences are that (a) we use the range acceleration observable, which then requires less filtering/regularization of the results, and (b) unlike the mascons in the solutions of the other centers, our variable‐shaped mascon geometry means that our mascons don't cross coastlines or the Amazon drainage boundaries (Tregoning et al., 2022). Our solution has been corrected for C 2,0 (Loomis et al., 2020), degree 1 ( tn13 a , Swenson et al., 2008; Sun et al., 2016), GIA (Peltier et al., 2018) and AOD1B‐GAD product (Dobslaw et al., 2017).…”

“…The observed differences can be attributed to the different processing methodology and definition of the mascons geometry (cf. our companion manuscript Tregoning et al, 2022). With the successful launch of the grace Follow-On mission in May 2018, including a more accurate laser to measure the inter-satellite range, the use of range acceleration observations offers the potential to improve significantly the recovery of the temporal gravity field.…”

“…We parameterize the temporal gravity field using mascons and derive changes in mass on each mascon in terms of an equivalent thickness of water over the area of the mascon. We explicitly relate the change in mass of each mascon directly to the inter‐satellite measurements, as described in our companion paper (Tregoning et al., 2022).…”

“…We derive partial derivatives relating our mascon parameters to the observations through an equation for the gravitational acceleration of two point sources, as described in Tregoning et al. (2022).…”

“…We parametrize the surface of the Earth in 12,721 mascons of about 40, 000 km 2 (roughly 200 km by 200 km, located on the ellipsoid) using the methodology of Tregoning et al. (2022). For the mascon solutions we also adopt an iterative process to refine the loads using basic linear least‐squares approach (Tarantola, 2005), $$${x}_{j}={x}_{j-1}+{({A}^{T}{C}_{D}^{-1}A+{C}_{M}^{-1}+{C}_{mass})}^{-1}({A}^{T}{C}_{D}^{-1}b).$$$ where x j are the adjustments to the a priori parameters x j −1 for iteration j , A is the design matrix of partial derivatives, C D is a diagonal weight matrix of the observations, C M is the constraint (or regularization) matrix, C mass is the conservation of mass constraint and b is the vector of prefit residuals.…”