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

Abstract

Small changes in the strength of the Earth's gravity field caused by the redistribution of mass on the Earth cause subtle changes in the range between the satellites. This is the fundamental observation that made the grace mission unique.A number of different mathematical approaches have been used to parameterize the Earth's gravity field and the convergence of the inversions of the data. Solving for coefficients of spherical harmonic models has been the most common approach used since the start of the grace mission (e.g., Lemoine et al., 2007;Tapley et al., 2004). A common characteristic of the estimated temporal gravity fields is a north-south striped error pattern, in part related to the high correlations between even and odd order coefficients (Swenson & Wahr, 2006

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

“…It is the range acceleration prefit residuals that were used as our inter-satellite observable when estimating the temporal gravity field. In our companion paper (Allgeyer et al, 2022), we demonstrated that using range acceleration information in this manner leads to a reduction in north/south striping in estimated gravity fields while also being able to spatially resolve both the low-and high-frequency components of the temporal gravity field.…”

“…No perturbations were applied to any of these satellite parameters in the simulations. We solved for adjustments to the initial satellite positions/velocities, accelerometer calibration scale factors and biases (one per axis per satellite per day), and adjustments to the mascons in terms of an equivalent height of water (of the appropriate density) in a least squares inversion of our simulated observations for each month (Allgeyer et al, 2022):…”

“…The ANU GRACE software used in the analysis can be downloaded from https://dx.doi.org/10.25911/61d-ceb9c03396. The time series of mascon estimates from the analysis of the Level-1B GRACE data are provided as part of Allgeyer et al (2022) and the mascon estimates can be accessed at https://dx.doi.org/10.25911/61d-ceb9c03396, along with a file containing the information linking ternary and primary mascons. The full global pattern of mass variation can be reconstructed from the time series of primary mascons by knowing the coordinates of the ternary mascons and assigning to each ternary mascon the temporal value of the primary mascon in which it resides.…”

“…We integrated satellite orbits for GRACE A and GRACE B, using accelerations computed from models and observations listed in Table 1 of Allgeyer et al. (2022). These orbits also included the accelerations induced by the temporal gravity field as represented on our ternary mascon field.…”

“…Range rate prefit residuals were formed, being the difference in range rate computed from the “truth” and a priori orbits. We then generated range acceleration prefit residuals by numerically differentiating the prefit range rate residuals (Allgeyer et al., 2022; Tregoning et al., 2017). It is the range acceleration prefit residuals that were used as our inter‐satellite observable when estimating the temporal gravity field.…”