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Summary Recent advances in the spatial and temporal retrieval of land-based cryospheric change information south of 42.5° allow fairly robust construction of forward model predictions of the time-rate of change in gravity. A map-view prediction is presented for the time-rate of change in geoid, dN/dt that might be retrieved from the currently orbiting gravity space craft, CHAMP (Challenging Mini-Satellite...
Summary We have used one year of CHAMP data for deriving a gravity field model based on the energy balance approach. In order to avoid the use of any a priori gravity information, purely kinematic orbits have been computed from GPS measurements only. Subsequently velocities have been derived from these kinematic positions by two different methods, namely smoothing splines and Newton- Gregory interpolation...
Summary This study investigates the effect of temporal gravity field variability on CHAMP and other geodetic satellites. The sensitivity of these satellites to the lower order and degree harmonics is presented along with the dominant tidal periodicities. Lumped harmonics from analyses of CHAMP are discussed with a singular value decomposition identifying the dominant combinations. Temporal variability...
Summary GPS-CHAMP satellite-to-satellite and accelerometry data covering 2.5 years of the CHAMP mission period were exploited to generate the global gravity field model EIGEN-3p revealing considerable improvements in both accuracy and resolution with respect to the previous model EIGEN-2. For the year 2001, CHAMP and satellite laser ranging data of four satellites were combined to recover largest...
Summary The operational Superconducting Gravimeter (SG) network can play an important role for validation of satellite-derived temporal gravity field variations. A comparison shows a quite good agreement between SG and CHAMP results within their estimated error bars. It could be proved that the SG-derived temporal gravity variations are representative for a large area within the µgal accuracy, if...
Summary The near-polar CHAMP and GRACE satellites are now acquiring vitally important new information on the geoid and gravity field of the polar regions. This investigation demonstrates that CHAMP and GRACE data are dramatically reducing the large gaps in our knowledge of the Arctic region, constraining the long wavelength geopotential (>300 km) and beginning to yield the high accuracy marine...
Summary This paper discussed consistency of long wavelength components of gravity field between the EGM96 and CHAMP gravity models and compared the long wavelength components of surface gravity data with ones from the models of CHAMP within the same spatial resolution, based on the 2-D Gaussian low-pass filter in China and its vicinity. The results show that the models of EGM96 and CHAMP are consistent...
Summary An extended Jacobi integral describes the energy balance of the motion of a satellite referred to a terrestrial reference frame along its orbit. In addition to its classical form inertia forces and non-conservative force function contributions are included. If force function models and observed satellite orbits are consistent the energy balance sums up to a constant. Deviations from it can...
Summary The new CHAMP and GRACE global gravity field models provide a significantly improved long wavelength gravity spectrum. These satellite-only models are therefore a good basis for studying long wavelength errors of the terrestrial gravity data, as they can be considered as a completely independent source of information. In this contribution, the models from the CHAMP and GRACE mission...
Summary The GeoForschungsZentrum Potsdam (GFZ) operationally provides CHAMP orbit products for various purposes. Here the rapid and ultra-rapid orbits are highlighted. Significant developments in Precise Orbit Determination (POD) for Low Earth Orbiters (LEOs), in particular SAC-C and GRACE besides CHAMP, are described. GFZ also started to generate CHAMP-like rapid orbits for SAC-C with good accuracy...
Summary The Rapid Science Orbit (RSO) is introduced into CHAMP gravity field processing as an auxilliary tool in order to facilitate the screening and to establish pre-estimated dynamical parameters, especially accelerometer calibration factors. It is furthermore shown how so-called pseudo-attitude angles help to edit the quaternions delivered by the CHAMP on-board star tracker cameras.
Summary This paper presents a synthesis of the CNES/GRGS routine activities regarding the analysis and calibration of the CHAMP accelerometer data. The impact of instrument operations and out of specification temperature variation on bias and scale factor estimation is demonstrated. Precise dynamic solutions of orbits and calibration parameters have been obtained from the processing of two years of...
Summary A new method to estimate CHAMP satellite-borne GPS receiver clock bias change is presented in this paper, according to the following approach. The difference between two neighboring epoch phase observations includes real CHAMP-GPS distance change, CHAMP clock receiver bias change, cycle slip and other corrections. Real CHAMP-GPS distance change can be obtained at a relatively high precision...
Summary Reduced-dynamic orbit determination for spaceborne GPS receivers is a method promising highest accuracy of the estimated LEO trajectories. We compare the performance of different pseudo-stochastic orbit parametrizations (instantaneous velocity changes and piecewise constant accelerations) and probe the range between dynamic and heavily reduced dynamic orbits. Internal indicators like formal...
Summary It is shown by means of an extensive simulation study as well as an experiment using real CHAMP data that it is feasible to accurately estimate non-conservative accelerations from precise GPS-based orbit perturbations. Assuming the availability of high-precision gravity field models, such as anticipated for GRACE and GOCE, an accuracy of better than 50 nm/s2 seems possible for 30-seconds averaged...
Summary The technique of using the evolution of a satellite orbit through resonance to determine the values of appropriate lumped geopotential harmonic coefficients has recently been revived, and applied to the triple passage of the Champ orbit through 31:2 resonance. Preliminary results for four pairs of coefficients have been derived rapidly, without using the most precise data (which will be forthcoming)...
Summary We report results on the use of CHAMP observations for Earth's mean and time-varying gravity field solutions and the associated geophysical interpretation. 1.5 years of CHAMP data from May 2001 through February 2003 are used for monthly gravity solutions as well as a mean solution based on 6 months of data, employing the energy conservation principle and an efficient conjugate gradient inversion...
Summary To obtain an alternative gravity solution to that of EIGEN1S, the author's Singular Value Decomposition(SVD) tool, Parallel LArge Svd Solver (PLASS), was applied to the CHAMP normal matrix ngl-eigen-1s {xc[2]} to perform an Eigenvalue Decomposition (EVD) analysis. The EIGEN1S solution is based on the Tikhonov regularization method of approximating the ill-conditioned system of equations in...
Summary Temporal variations of the gravity field may act either as a signal or as a source of noise for the current satellite gravity missions. This depends, to some extent, on the parametrization of the gravity field solution. We discuss qualitatively how temporal variations affect satellite gravity products and how their effects may be controlled by an adequate parametrization. We describe a mechanism...
Summary The gravity field recovery strategy presented here enables the global recovery of the gravity field combined with a regional focus on geographical areas with rough gravity field features in a consistent way. The global gravity field is modeled by a series of spherical harmonics while the regional gravity field features are represented by space localizing base functions of harmonic spline type...
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