Abstract
After it was found that the gravity gradients observed by the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite could be significantly improved by an advanced calibration, a reprocessing project for the entire mission data set was initiated by ESA and performed by the GOCE High-level processing facility (GOCE HPF). One part of the activity was delivering the gravity field solutions, where the improved level 1b and level 2 data serve as an input for global gravity field recovery. One well-established approach for the analysis of GOCE observations is the so-called time-wise approach. Basic characteristics of the GOCE time-wise solutions is that only GOCE observations are included to remain independent of any other gravity field observables and that emphasis is put on the stochastic modeling of the observations’ uncertainties. As a consequence, the time-wise solutions provide a GOCE-only model and a realistic uncertainty description of the model in terms of the full covariance matrix of the model coefficients. Within this contribution, we review the GOCE time-wise approach and discuss the impact of the improved data and modeling applied in the computation of the new GO_CONS_EGM_TIM_RL06 solution. The model reflects the Earth’s static gravity field as observed by the GOCE satellite during its operation. As nearly all global gravity field models, it is represented as a spherical harmonic expansion, with maximum degree 300. The characteristics of the model and the contributing data are presented, and the internal consistency is demonstrated. The updated solution nicely meets the official GOCE mission requirements with a global mean accuracy of about 2 cm in terms of geoid height and 0.6 mGal in terms of gravity anomalies at ESA’s target spatial resolution of 100 km. Compared to its RL05 predecessor, three kinds of improvements are shown, i.e., (1) the mean global accuracy increases by 10–25%, (2) a more realistic uncertainty description and (3) a local reduction of systematic errors in the order of centimeters.
Highlights
More than ten years ago, the dedicated gravity field mission Gravity field and steady-state Ocean Circulation Explorer (GOCE) was launched to its science orbit by the European Space Agency (ESA) on March 17, 2009
Based on the reprocessed gravity gradients of the GOCE mission and using an advanced processing approach, the new global gravity field model GO_CONS_EGM_TIM_RL06 was computed as a successor of the RL05 model published in 2014. It follows the philosophy of the previous GOCE time-wise models, with the basic idea that it is based on GOCE observations only
As typically for global gravity field models, it is provided as a spherical harmonic expansion, truncated at degree 300
Summary
More than ten years ago, the dedicated gravity field mission Gravity field and steady-state Ocean Circulation Explorer (GOCE) was launched to its science orbit by the European Space Agency (ESA) on March 17, 2009. As the space-wise models, the time-wise approach uses only GOCE observations to derive an independent model of the Earth’s gravity field as it was measured by the GOCE satellite. Using empirical auto-covariance functions and variance component estimation in addition to the covariance matrix of the kinematic positions, a refined data adaptive stochastic model for the kinematic orbit positions is used This results in a more realistic covariance matrix of the resulting SSThl solution, which later controls the relative weighting when combined with the normal equations assembled from the gravity gradients. Several authors applied similar approaches compared to the time-wise and the direct approach They set up the least-squares observation equations in the GRF, but the way that the correlations are modeled and relative weights are estimated differs (e.g., Yi et al 2013; Schall et al 2014; Wu 2016; Xu et al 2017).
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