Advanced GRACE accelerometer sensor analysis, impact on gravity field determination and aeronomy research
Zusammenfassung der Projektergebnisse
GRACE is a geodetic Earth observation satellite mission measuring variations in the Earth's gravity field and in global mass distribution. Launched in 2002, the mission is expected to extend until about the year 2012. GRACE observes the range between a pair of twin satellites with a microwave ranging system with micrometer precision. In addition, non-gravitational forces acting on the satellites are observed by accelerometers with a measurement precision of 10-10 m/s2. From GRACE observations, a wealth of new and fascinating results on mass changes in the Earth system have been obtained: mass loss by melting of the Greenland and Antarctica ice sheets has been quantified, mass changes in the ocean circulation system and in the hydrological cycle have been determined, and mass shifts in crust and mantle of the Earth have been detected. However, the measurement precision of the novel sensors on GRACE is not fully exploited as of today. This is in part due to the fact that GRACE sensor observations are super-imposed by noise-like signal components which were previously not understood in detail. In this project, it was shown that a large part of the pseudo-noise is related to satellite-induced disturbances. Several types of disturbances were identified: effects due to electrical switching of heater elements, effects due to electrical currents in magnetic torquer rods, and vibrationlike effects related to influence of solar radiation on the satellites. Empirical models for these effects were developed - modeling efforts are ongoing - and the effects were successfully separated. Modeling and separation are important for the understanding of disturbance mechanisms, for the investigation of their influence on gravity field determination, and for monitoring of sensor precision. Such issues are expected to have a growing importance for future satellite missions. Future sensors on new precision levels - such as laser interferometry between satellites - will also require to monitor, understand and model disturbances on a new level.
Projektbezogene Publikationen (Auswahl)
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(2007) Heights in the Bavarian Alps: Mutual validation of GPS, levelling, gravimetric and astrogeodetic quasigeoids, Proceedings GRF2006
Flury J, Gerlach C, Hirt C, Schirmer U
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(2007) Micro-accelerations due to heater switches on board the GRACE satellites observed by the SuperSTAR accelerometers. CSR Report, University of Texas
Flury J, Bettadpur S
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(2007) Precision gravimetry in the new Zugspitze calibration system, Proceed IGFS06
Flury J, Peters T, Schmeer M, Timmen L, Wilmes H, Falk R
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(2007) Satellite-induced spike features in the GRACE accelerometer observations. Technical Note, CSR, University of Texas
Flury J
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(2008) Astronomical-topographic levelling using high-precision astro-geodetic vertical deflections and DTM data. J Geod 82(4-5):231-248
Hirt C, Flury J
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(2008) Hochpräzise Bestimmung eines astrogeodätischen Quasigeoidprofils im Harz für die Validierung des GCG05, Z f Vermessungswesen 133(2):108-119
Hirt C, Feldmann-Westendorff U, Denker H, Flury J, Jahn CH, Lindau A, Seeber G, Voigt C
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(2008) Precise accelerometry onboard the GRACE gravity field satellite mission, Adv Space Res 42:1414–1423
Flury J, Bettadpur S, Tapley B
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(2009) On the geoid - quasigeoid separation in mountain areas. J Geod
Flury J, Rummel R
