The main objective of the GOCE mission is to determine the static part of the Earth’s gravity field with unprecedented accuracy and spatial resolution. As opposed to the original schedule, it turned out that it is technically feasible to probe the Earth’s gravity field continuously also during the long eclipse (hibernation) phases, and due to the mission extension until December 2012 even for a much longer time period. In this feasibility study a first analysis shall be done (a) to what extent GOCE can support and improve timevariable GRACE gravity field estimates, and (b) if the GOCE orbit information alone is sensitive enough to detect temporal gravity signals. Comparing a combined temporal gravity model from GRACE and GOCE with a pure GRACE-only solution, it turns out that GOCE indeed has the potential to improve the solution by reducing the typical GRACE striping pattern significantly. GOCE-only temporal gravity field solutions based on kinematic precise orbits seem feasible for the very low degrees, presuming that the systematic errors in current solutions could be reduced, and longer GOCE orbit time series were available.

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).

After the annexation of Austria into the German Reich the “Berufsordnung der Offentlich bestellen Vermessungsingenieure“ (ObVI) was introduced in 1940. By analysis of documents in the German Federal Archives (Berlin) statements about the political orientation of the profession and the licensing procedure are possible. Within the group of ObVI the former “Ingenieurkonsulenten fur Vermessungswesen“ were the third largest group. The surveyors had to take the licensing procedure or they had to close their offices. The number of finally approved ObVI's is significantly lower than the number of independent surveyors in Austria in 1938. The result of the approval process was like in German Empire since 1938 a market adjustment. As part of the process, the political reliability and the ancestry of the candidates has been verified. In some cases, the authorization was denied for political reasons. In most cases, the rejection was based on age or lack of skills.

The main objective of the GOCE mission is to determine the static part of the Earth’s gravity field with unprecedented accuracy and spatial resolution. As opposed to the original schedule, it turned out that it is technically feasible to probe the Earth’s gravity field continuously also during the long eclipse (hibernation) phases, and due to the mission extension until December 2012 even for a much longer time period. In this feasibility study a first analysis shall be done (a) to what extent GOCE can support and improve timevariable GRACE gravity field estimates, and (b) if the GOCE orbit information alone is sensitive enough to detect temporal gravity signals. Comparing a combined temporal gravity model from GRACE and GOCE with a pure GRACE-only solution, it turns out that GOCE indeed has the potential to improve the solution by reducing the typical GRACE striping pattern significantly. GOCE-only temporal gravity field solutions based on kinematic precise orbits seem feasible for the very low degrees, presuming that the systematic errors in current solutions could be reduced, and longer GOCE orbit time series were available.

The satellite mission GOCE (Gravity and steady-state Ocean Circulation Explorer) has the demanding task to map the Earth’s gravity field with unprecedented accuracy by using state-of-the-art observation technologies. The processing strategy of the orbit data is based on the energy integral approach to determine the long wavelength structure of the gravity field. The final product will consist of the gravity field model in terms of estimated spherical harmonic coefficients and the corresponding error description. The study about covariance propagation of latitude-dependent orbit errors is driven by the fact that the GPS receiver used for GOCE might not have full performance in the case of low-elevation GPS satellites, which might lead to a reduced number of observable satellites in higher latitudes. Therefore, the adjustment procedure is extended by a covariance propagation taking this fact into account. The studies have shown that the consistent error propagation can not significantly improve the coefficient solution itself but it rather provides a correct error description of the result.

A first GOCE gravity field model based on two months of GOCE orbit and gradiometry data has been computed applying the time-wise method. The paper gives an overview of the software system, and discusses the key features of the solution strategy. The resulting global gravity field model, resolved complete to degree/order 224, is GOCE-only in a strict sense, i.e., no a priori gravity field information entered the solution. Realistic stochastic models for both the orbit and gradiometer observations have been included. Thus, the coefficient error information, provided as full variance-covariance matrix, reflects the true error behaviour of the solution. The resulting GOCE model is assessed and validated against state-of-the art gravity field models. Since the model is independent of any gravity prior information, it can be used to assess the additional information content of GOCE, and can be combined with complementary satellite and terrestrial gravity field information.

The satellite‐only gravity field model GOCO01S is a combination solution based on 61 days of GOCE gravity gradient data, and 7 years of GRACE GPS and K‐band range rate data, resolved up to degree/order 224 of a harmonic series expansion. The combination was performed consistently by addition of full normal equations and stochastic modeling of GOCE and GRACE observations. The model has been validated against external global gravity models and regional GPS/leveling observations. While low to medium degrees are mainly determined by GRACE, significant contributions by the new measurement type of GOCE gradients can already be observed at degree 100. Beyond degree 150, GOCE becomes the dominant contributor. Correspondingly, with GOCO01S a global gravity field model with high performance for the complete spectral range up to degree/order 224 is now available. This new gravity model will be beneficial for many applications in geophysics, oceanography, and geodesy.

Satellite gravity field missions such as CHAMP, GRACE and GOCE are designed as low Earth orbiting spacecraft (LEO) with orbit heights of about 250-500 km. The challenging mission objectives require a very precise knowledge of the satellite orbit position in space. For these missions precise orbit information is typically provided by GPS satellite-to-satellite tracking (SST) observations supported by satellite laser ranging (SLR).The role of SLR is primarily devoted to serve as an independent tracking instrument used to calibrate and validate the on-board GPS flight receiver. However, the very limited visibility of LEOs from SLR ground stations together with the accordingly high angular rates necessary for the laser mounting to follow the satellite make it more difficult to track LEO missions. At the Observatory Graz Lustbuhel, the Space Research Institute of the Austrian Academy of Sciences operates a very novel SLR facility which was continuously upgraded during the recent years, and is today the only station worldwide capable to operate at kHz-firing rates. The activities presented here focus on a number of hardware upgrades and methodical improvements at the SLR station Graz aiming for a faster and more reliable target acquisition. These include upgrades of laser tracking algorithms as well as a redesign of the laser detection package in particular for LEO spacecraft. These improvements allow an extension of the measurement durations and thus increase the number of observations per pass. As a result we are able to raise the normal point accuracy as well as the overall system performance for LEO tracking. Improvements of the pointing accuracy and the range gate control system lead to a data quantity raise of about 5%.Another task addresses both a geometric and dynamic arc comparison of SLR derived orbits with GPS SST orbit solutions. In the case of CHAMP, the resulting one-way SLR range residuals are in the order of a few centimetres. This allows to draw conclusions on the accuracy of orbit solutions. In order to evaluate the performance of this technique for the upcoming GOCE mission, investigations are carried out in an analogous manner based on simulated GOCE SLR observations.In this study, it is demonstrated that satellite laser ranging, in particular with high-rate tracking capabilities and low orbit optimizations, offers a valuable tool for orbit validation purposes. (C) 2010 Published by Elsevier Ltd. on behalf of COSPAR.