An Improved Model of the Earth’s Static Gravity Field Solely Derived from Reprocessed GOCE Data

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.

Mean Dynamic Topography Modeling Based on Optimal Interpolation from Satellite Gravimetry and Altimetry Data

“…In order to facilitate the estimation of errors of the geoid, this study introduces multigeneration, GOCE-derived GGMs solved by the direct and time-wise approaches: the GO_CONS_GCF_2_DIR_R4 (DIRR4), GO_CONS_GCF_2_DIR_R5 (DIRR5), and GO_CONS_GCF_2_DIR_R6 (DIRR6); and the GO_CONS_GCF_2_TIM_R4 (TIMR4), GO_CONS_GCF_2_TIM_R5 (TIMR5), and GO_CONS_GCF_2_TIM_R6 (TIMR6) [9,19]. Table 1 summarizes detailed information about these GOCE-derived GGMs.…”

GOCO06s – A satellite-only global gravity field model

“…Furthermore, due to the use of an advanced stochastic model for the gravity gradients during the assembly of the satellite gravity gradient (SGG) normal equations, the formal errors are a realistic description of the uncertainties, which is beneficial for the combination procedure. Within GOCO06s, normal equations from the time-wise RL06 model (GO_CONS_EGM_TIM_RL06, Brockmann et al, 2019;Brockmann et al, 2021) are used, which are based on SGG observations of the latest reprocessing campaign in 2019. A single unconstrained normal equation assembled from the V XX , V XZ , V Y Y and V ZZ gravity gradient observations up to spherical harmonic degree 300 enters the computation of GOCO06s (see Sect.…”

“…It is the same normal equation as used in GO_CONS_EGM_TIM_RL06, which is in the context of a GOCE-only model combined with SST-hl data and constrained (cf. Brockmann et al, 2021).…”

“…In addition, an independent SLR/GRACE/GOCE satellite-only combination model, namely GOCE-DIR6 (Förste et al, 2019), is used for comparisons, which to a large extent is based on the same amount of SLR, GRACE and GOCE data as GOCO06s. In order to identify the performance of pure GRACE and pure GOCE models compared to the combined GOCO06s model, the ITSG-Grace2018s (Kvas et al, 2019a) model and the GOCE-TIM6 (Brockmann et al, 2019;Brockmann et al, 2021) model are applied to the validation procedure. Finally, a model combining the GOCO06s satellite data with surface, airborne and altimetric gravity data is used in order to identify the signal content in higher degrees of the GOCO06s model.…”

“…These models are closely related to the GOCE solutions determined with the direct approach, which are already combination models (Bruinsma et al, 2014(Bruinsma et al, , 2013. Basically, GRACE normal equations processed by CNES/GRGS (Bruinsma et al, 2010) or GFZ (Dahle et al, 2019) are combined with GOCE normal equations assembled with the so-called direct approach (Bruinsma et al, 2014;Pail et al, 2011) and SLR normal equations. The combination is performed on the normal equation level.…”