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See detailOn the capability of non-dedicated GPS-tracked satellite constellations for estimating mass variations: case study SWARM
Reubelt, T.; Baur, O.; Weigelt, Matthias UL et al

Scientific Conference (2013, September)

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See detailTime-variable gravity signal in Greenland revealed by high-low satellite-to-satellite tracking
Weigelt, Matthias UL; van Dam, Tonie UL; Jäggi, Adrian et al

in Journal of Geophysical Research. Solid Earth (2013), 118

In the event of a termination of the GRACE mission before the launch of GRACE Follow-On (due for launch in 2017) high-low satellite-to-satellite tracking (hl-SST) will be the only dedicated observing ... [more ▼]

In the event of a termination of the GRACE mission before the launch of GRACE Follow-On (due for launch in 2017) high-low satellite-to-satellite tracking (hl-SST) will be the only dedicated observing system with global coverage available to measure the time variable gravity field (TVG) on a monthly or even shorter time scale. Until recently, hl-SST TVG observations were of poor quality and hardly improved the performance of Satellite Laser Ranging observations. To date, they have been of only very limited usefulness to geophysical or environmental investigations. In this paper, we apply a thorough reprocessing strategy and a dedicated Kalman filter to CHAMP data to demonstrate that it is possible to derive the very long wavelength TVG features down to spatial scales of approximately 2000 km at the annual frequency and for multi-year trends. The results are validated against GRACE data and surface height changes from long-term GPS ground stations in Greenland. We find that the quality of the CHAMP solutions is sufficient to derive long-term trends and annual amplitudes of mass change over Greenland. We conclude that hl-SST is a viable source of information for TVG and can serve to some extent to bridge a possible gap between the end-of-life of GRACE and the availability of Grace Follow-On. [less ▲]

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See detailA new variant of the differential gravimetry approach
Weigelt, Matthias UL; van Dam, Tonie UL; Bandikova, T.

Scientific Conference (2013, June)

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See detailOn the numerical stability in the derivation of Slepian base functions
Weigelt, Matthias UL; van Dam, Tonie UL; Wang, Lin UL

Scientific Conference (2013, June)

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See detailDerivation of angular velocities of the GRACE satellite formation from the star camera data
Bandikova, T.; Weigelt, Matthias UL; van Dam, Tonie UL et al

Scientific Conference (2013, June)

The presentation discusses possibilites to derive common frame angular velocities from the star cameras in the GRACE system. Generally the star cameras measure the rotation of each satellite independently ... [more ▼]

The presentation discusses possibilites to derive common frame angular velocities from the star cameras in the GRACE system. Generally the star cameras measure the rotation of each satellite independently from the other satellite. However, common frame rotations are also needed for various applications. Specifically in this presentation we discuss the application to a variant of the differential gravimetry approach. In this, angular rates around the crosstrack component of the so-called instantaneous relative reference frame are needed. The latter is a common reference frame formed by the inter-satellite connection of the two GRACE satellites. We will quantify the accuracy demands on the derivation of the angular velocities and discuss the possibilites to meet these demands with existing star camera observations. We will also give an outlook on new possibilites in the determination of the orientation and the derivation of angular velocities offered by the laser ranging instrument which will be used in the GRACE Follow-On mission. [less ▲]

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See detailLong-term mass changes over Greenland derived from high-low satellite-to-satellite tracking
Weigelt, Matthias UL; van Dam, Tonie UL; Jäggi, Adrian et al

Poster (2013, April)

In the last decade, temporal variations of the global gravity field have become an ubiquitous and invaluable source of information for geophysical and environmental studies. It is important that the time ... [more ▼]

In the last decade, temporal variations of the global gravity field have become an ubiquitous and invaluable source of information for geophysical and environmental studies. It is important that the time series of observations is not interrupted as some geophysical phenomena, e.g. postglacial rebound or long term ice mass trends, are only beginning to be observable. To date, the most valuable source for time variable gravity (TVG) is the GRACE mission which has already exceeded its nominal lifetime. It can cease operations any time now and then only high-low satellite-to-satellite (hl-SST) observations will be available. These observations have, however, only demonstrated limited application for TVG. In this presentation, we show that by using CHAMP data, a thorough reprocessing strategy and a dedicated Kalman filter it is possible to derive the very long wavelength features of the time variable gravity field. The results are validated against GRACE data and height coordinates from long-term GPS ground stations in Greenland. We find that the quality of the CHAMP solutions is sufficient to derive realistic long-term trends and annual amplitudes of mass changes of Greenland. We conclude that hl-SST would be a viable substitute (although at lower spatial resolution) for TVG in the event of a profund operational breakdown of GRACE. [less ▲]

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See detailHydrological mass changes inferred from high-low satellite-to-satellite tracking data
van Dam, Tonie UL; Weigelt, Matthias UL; Tourian, M. J. et al

Scientific Conference (2013, April)

The technique of deriving time variable gravity (TVG) field observations from high-low satellite-to-satellite tracking (hl-SST) is beginning to establish itself as a valuable and supplementary source for ... [more ▼]

The technique of deriving time variable gravity (TVG) field observations from high-low satellite-to-satellite tracking (hl-SST) is beginning to establish itself as a valuable and supplementary source for the determination and description of long wavelength geophysical phenomena. Recent developments in data processing techniques have pushed the limits of the accuracy of these types of observations and now allows for realistic determinations of long-term trends and annual amplitudes of hydrological signals. We use CHAMP data and a dedicated signal processing to derive annual and inter-annual variations in the largest catchments of the Earth system, e.g. Amazon, Ob and Lena. Results are validated by computing the correlation of aggregated water storage changes from CHAMP (and GRACE) with the hydro-meteorological storage changes. High noise levels demand a stronger filtering, e.g. larger filtering radius (1000-1400km), than usually applied in case of GRACE. We therefore also investigate the effect of filtering on the consistency with the hydrological mass changes and estimate the signal to noise ratio and the spatial and temporal dependency of the noise. We will show that hl-SST observations are a viable source of information for TVG which can even serve as a reliable substitute in the event of the impending end of GRACE's active lifetime. [less ▲]

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See detailAn improved sampling rule for mapping geopotential functions of a planet from a near polar orbit
Weigelt, Matthias UL; Sneeuw, Nico; Schrama, E.J.O. et al

in Journal of Geodesy (2013), 87(2), 127-142

One of the limiting factors in the determination of gravity field solutions is the spatial sampling. Especially during phases, when the satellite repeats its own track after a short time, the spatial ... [more ▼]

One of the limiting factors in the determination of gravity field solutions is the spatial sampling. Especially during phases, when the satellite repeats its own track after a short time, the spatial resolution will be limited. The Nyquist rule-of-thumb for mapping geopotential functions of a planet, also referred to as the Colombo–Nyquist rule-of-thumb, provides a limit for the maximum achievable degree of a spherical harmonic development for repeat orbits. We show in this paper that this rule is too conservative, and solutions with better spatial resolutions are possible. A new rule is introduced which limits the maximum achievable order (not degree!) to be smaller than the number of revolutions if the difference between the number of revolutions and the number of nodal days is of odd parity and to be smaller than half the number of revolutions if the difference is of even parity. The dependence on the parity is reflected in the eigenvalue spectrum of the normal matrix and becomes especially important in the presence of noise. The rule is based on applying the Nyquist sampling theorem separately in North–South and East–West direction. This is only possible for satellites in highly inclined orbits like champ and grace. Tables for these two satellite missions are also provided which indicate the passed and (in case of grace) expected repeat cycles and possible degradations in the quality of the gravity field solutions. [less ▲]

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See detailGOCE long-wavelength gravity field recovery from 1s-sampled kinematic orbits using the acceleration approach
Reubelt, T.; Baur, O.; Weigelt, Matthias UL et al

in GGHS2012 - Gravity, Geoid and Height Systems 2012 (2013)

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See detailTime variability from high-low SST - filling the gap between GRACE and GFO
Weigelt, Matthias UL; Jäggi, A.; Prange, L. et al

Scientific Conference (2012, October)

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See detailOn the capability of SWARM for estimating time-variable gravity fields and mass variations
Reubelt, T.; Baur, O.; Weigelt, Matthias UL et al

Poster (2012, October)

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See detailLarge scale time variability from high-low SST - filling the gap between GRACE and GFO
Weigelt, Matthias UL; van Dam, Tonie UL; Jäggi, A. et al

Scientific Conference (2012, September)

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See detailGOCE orbit analysis: Long-wavelength gravity field determination using the acceleration approach
Baur, O.; Reubelt, T.; Weigelt, Matthias UL et al

in Advances in Space Research (2012), 50(3), 385--396

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See detailSind wir fur zukunftige Schwerefeldmissionen gerüstet?
Weigelt, Matthias UL

Presentation (2012, April)

Detailed reference viewed: 13 (1 UL)