Improving the accuracy of the spherical harmonic coefficients of the Earth’s gravity field and its temporal variations at long and medium spatial-scales with unprecedented accuracy is the primary science objective of the GRACE mission. The line of sight (LOS) acceleration difference between the satellite pair is the most frequently utilized form of the observable. It is the simplest form of the observable which can be easily employed. Nevertheless, the observable is a two-point function and has no direct relationship with the field geometry at the evaluation point.
In this paper, as the alternative, gradiometry approach is proposed. Being a one-point function and having a direct relation with the field geometry (curvature of the field at the point) are two noteworthy achievements of the alternative formulation. Besides, using an observation quantity that is related to the second instead of the first-order derivatives of the gravitational potential amplifies the high-frequency part of the signal.
Complexity of the derived mathematical model and its proper treatment is the severe problem for the gradiometry approach. Herein, mixed gravitational acceleration-gradient model and also use of the available Earth’ gravity model as a priori information on the low-degree harmonics are addressed.
The first recently released EIGEN2 CHAMP-only Earth’s gravity model was employed for numerical analysis. Error analysis showed that the residuals of the estimated degree variances were of about 10−4 for n≤ 90. Also, the gravity anomaly residuals were less than 5 mGal for most points on the Earth.
KeywordsGRACE Gradiometer Gradiometry Sequential solution
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