Search

The impact of GOCE Satellite Gravity Gradiometer data on gravity field models was tested. All models were constructed with the same Laser Geodynamics Satellite (LAGEOS) and Gravity Recovery and Climate Experiment (GRACE) data, which were combined with one or two of the diagonal gravity gradient components for the entire GOCE mission (November 2009 to October 2013). The Stokes coefficients were estimated by solving large normal equation (NE) systems (i.e., the direct numerical approach). The models were evaluated through comparisons with the European Space Agency's (ESA) gravity field model DIR-R5, by GPS/Leveling, GOCE orbit determination, and geostrophic current evaluations. Among the single gradient models, only the model constructed with the vertical ZZ gradients gave good results that were in agreement with the formal errors. The model based only on XX gradients is the least accurate. The orbit results for all models are very close and confirm this finding. All models constructed with two diag...

[1] Reprocessed Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) gravity gradient data were combined with data from Laser Geodynamics Satellite (LAGEOS) 1/2 and Gravity Recovery and Climate Experiment (GRACE) to generate a satellite-only gravity field model to degree 260 using the direct approach, named DIR-R4. When compared to Earth Gravitational Model 2008 (EGM2008), it is more accurate at low to medium resolution thanks to GOCE and GRACE data. When compared to earlier releases of ESA GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested. It is also slightly more accurate than ESA's fourth release of the time-wise model (TIM-R4), as demonstrated by GPS/leveling, orbit determination tests, and an oceanographic evaluation. According to the formal, probably too optimistic by a factor of 2–2.5, cumulated geoid (1.3 cm) and gravity anomaly (0.4 mGal) errors at 100 km resolution, the GOCE mission objectives have been reached.

A set of linear harmonic Junctions was obtained as a special solution of the Laplace equation and was used as a basis of the non-orthogonal functions for approximation of the gravitational potential Maxwell method was applied to the construction of such a set of the linear harmonic functions. Resulting formulas were obtained in the form of the finite sums that provides the practical constructions of a new set of linear harmonic functions for global and regional gravity field description. В качестве неортогональных базисных функций для аппроксимации гравитационного потенциала планет используется семейство линейных гармонических функций, полученных на основании специального решения уравнения Лапласа. Для их построения использован метод Максвелла. Полученные таким образом формулы, в виде конечных сумм, позволяют практически реализовать построение нового семейства линейных гармонических функций для использования при аппроксимации гравитационного потенциала планет в глобальном и региональном масштабах. В якості неортогональних базисних функцій для апроксимації гравітаційного потенціалу планет використано сімейство лінійних гармонічних функцій, отриманих на основі спеціального розв 'язку рівняння Лапласа. Для його побудови використано метод Максвела. Отримані таким чином формули, у вигляді скінчених сум, дозволяють практично реалізувати побудову нового сімейства лінійних гармонічних функцій для використання при апроксимації гравітаційного потенціалу планет в глобальному і регіональному масштабах.

Gravity field and steady state Ocean Circulation Explorer (GOCE) gravity gradient data of the entire science mission and data from LAGEOS 1/2 and Gravity Recovery and Climate Experiment (GRACE) were combined in the construction of a satellite-only gravity field model to maximum degree 300. When compared to Earth Gravitational Model 2008, it is more accurate at low to medium resolution, thanks to GOCE and GRACE data. When compared to earlier releases of European Space Agency GOCE models, it is more accurate at high degrees owing to the larger amount of data ingested, which was moreover taken at lower altitude. The impact of orbiting at lower altitude in the last year of the mission is large: a model based on data of the last 14 months is significantly more accurate than the release 4 model constructed with the first 28 months. The (calibrated) cumulated geoid error estimate at 100 km resolution is 1.7 cm. The optimal resolution of the GOCE model for oceanographic application is between 100 and 125 km.

Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10 cm in terms of geoid heights, and 3 mGal in terms of gravity anomalies, globally at a resolution of 100 km (degree/order 200).

The recently launched GOCE mission will set a new milestone in gravity field determination. Due to the high accuracy of its gradiometry observations, the resulting satellite-only Earth gravity models will have a resolution of up to degree/order 250, with an expected accuracy of 1–2 cm in terms of geoid heights. In order to increase this resolution up to at least 360, a combination with surface data is necessary. In the following article the strategies for this combination developed at GFZ, Helmholtz-Zentrum Potsdam, are outlined and discussed. Basically two approaches for the combination exist; the first uses complete and block-diagonal normal equations, while the other uses complete normal equations only. In this article, both approaches are explained with their pros and cons, and the GFZ-strategy is presented at its current stage for the combination of GOCE with GRACE and surface data.