GECO: a global gravity model by locally combining GOCE data and EGM2008

Abstract

The EGM2008 model is nowadays one of the description of the global gravitational field at the highest resolution. It is delivered with two, not fully consistent, sources of information on its error: spherical harmonic coefficient variances and a geographical map of error variances, e.g. in terms of geoid undulation. In the present work, the gravity field information derived from a GOCE satellite-only global model is used to improve the accuracy of EGM2008 model in the low to medium frequencies, especially in areas where no data were available at the time of EGM2008 computation. The key issue is to set up the error covariance matrices of the two models for an optimal least-squares combination: the full error covariance matrix of GOCE spherical harmonic coefficients is approximated by an order-wise block-diagonal matrix, while for EGM2008, the pointwise error variances are taken from the provided geoid error map and the error spatial correlations from the coefficient variances. Due to computational reasons the combination is directly performed in terms of geoid values over a regular grid on local areas. Repeating the combination for overlapping areas all over the world and then performing a harmonic analysis, a new combined model is obtained. It is called GECO and extends up to the EGM2008 maximum degree. Comparisons with other recent combined models, such as EIGEN-6C4, and a local geoid based on new gravity datasets in Antarctica are performed to evaluate its quality. The main conclusion is that the proposed combination, weighting the different input contributions not only on a global basis but also according to some local error information, can perform even better than other more sophisticated combinations in areas where the input global error description is not reliable enough

The first Australian gravimetric quasigeoid model with location-specific uncertainty estimates

“…Two degree-2190 EGMs have been released since EGM2008: EIGEN-6C4 (Förste et al 2015) and GECO (Gilardoni et al 2015), both of which include GRACE (Tapley et al 2004) and GOCE (Drinkwater et al 2003) data. [EGM2008 only includes GRACE data].…”

Moho Depth and Crustal Architecture Beneath the Levant Basin from Global Gravity Field Model

“…In this section, the results of this reduction are presented. The gravity field data have been synthesized from the GECO (GOCE and EGM2008 COmbined) model [28], which is basically a combination of GOCE and EGM2008 [29] data. In detail, the spherical harmonics of the GECO model have been synthesized in terms of gravity anomalies, on a grid of a constant altitude of 3500 m with a spatial resolution of 1 arc-min, which coincides to about 1.5 km in the West-East direction and 1.8 km in the South-North one.…”

Towards the Selection of an Optimal Global Geopotential Model for the Computation of the Long-Wavelength Contribution: A Case Study of Ghana

“…We use the Earth Gravitational Model 2008, EGM2008 [13], and the fifth releases of the direct, DIR-R5 [12], and time-wise, TIM-R5 [11] solutions of the Gravity field and steady-state Ocean Circulation Explorer (GOCE); and GOCE and EGM2008 Combined Model, GECO [15]. These are available online at http://icgem.gfz-potsdam.de/home.…”