Calibration of CHAMP Accelerometer Observations for Precise Determination of insitu Gravity Measurements

Yiqun Chen, S.-C. Han, Burkhard Schaffrin and C.K. Shum

Abstract:	The instruments onboard the CHAllenging Minisatellite Payload (CHAMP) include geodetic-quality, Blackjackclass, GPS receivers for precise orbit determination and a 3-axis Space Triaxial Accelerometer for Research (STAR) to measure non-conservative forces. These instruments are essential for precise orbit determination and gravity field estimation. However, it is necessary to correct well-known systematic errors such as constant bias, scale factor, and drift in the accelerometer data. The calibration cannot be implemented under the 1-g ground environment, it rather needs to be done in flight. There are several approaches to do this, for example, either by comparing observed non-conservative forces with the ones computed from the corresponding models, or during the process of gravity field estimation and orbit improvement. In this investigation we use a more direct method for the accelerometer calibration. We compute the 3-D non-conservative force vectors based on the kinematic acceleration of CHAMP and a reference gravity model, and then compare the computed non-conservative forces with the ones observed by the 3-D STAR. The difference between them indicates the practical imperfect performance of the accelerometer instrument. The observations are adjusted to the computed values, and the corresponding constant bias and drift factors in each axis are estimated in a least-squares sense. The results indicate that the constant biases are about 0.750mgal (in the radial direction), -0.353mgal (in the along-track direction) and 0.047mgal (in the cross-track direction). They are comparable to the results obtained from precise orbit determination (Kang et al. 2003) and other methods (Han et al. 2002), in which the calibration parameters were estimated using completely independent and different methods. After we have verified and calibrated the accelerometer observable, we determine the in-situ gravitational force vector at altitude by combining the kinematic acceleration and (calibrated) non-conservative acceleration. We then validate our in-situ gravity vectors based on the state-of-the-art recent gravity field models including EGM96, EIGEN2 and GGM01S; the results are reasonable.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	505 - 512
Cite this article:	Chen, Yiqun, Han, S.-C., Schaffrin, Burkhard, Shum, C.K., "Calibration of CHAMP Accelerometer Observations for Precise Determination of insitu Gravity Measurements," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 505-512.
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