HR: 1340h
AN: G33A-0891    [Abstracts]
TI: GOCE gradiometer: estimation of bias and scale factors of all 6 individual accelerometers by precise orbit determination
AU: * Visser, P N
EM: P.N.A.M.Visser@tudelft.nl
AF: Delft Institute of Earth Observation and Space Systems (DEOS), Kluyverweg 1, Delft, 2629 HS, Netherlands
AB: The GOCE gradiometer ideally consists of an orthogonal triad of three pairs of accelerometers. A method has been developed and implemented for the estimation of absolute calibration parameters, such as accelerometer biases, bias drifts and scale factors by precise orbit determination. The method was applied to a test data set of simulated GOCE observations. Concerning the accelerometers, the following error sources were taken into account: frequency dependent observation noise, misalignments of the axes of the individual accelerometers, quadratic terms, non-orthogonalities, biases and bias drifts, and scale factor errors. The orientation of the accelerometers is derived from star tracker observations, that were affected by realistic errors as well. It was found that the observations taken by individual accelerometers needed to be corrected for local satellite gravity gradient and rotational terms (i.e. caused by centrifugal and angular accelerations) due to their offset location with respect to the satellite center of mass. These corrections were found to be sufficiently adequate when using a simple reference gravity field model and derive the rotational terms from the star tracker observations. However, for an accurate determination of the accelerometer scale factors is was found that a high-precision gravity field is required in the orbit determination itself or that gravity field coefficients need to be co-estimated (making the procedure computationally demanding, but still feasible). It was found that with a high-quality a priori gravity field model and with the co-estimation of not only biases but also bias drifts, scale factors can be determined with an accuracy better than 0.01 for two of the three axes of each accelerometer, the exception being the axis pointing along the long axis of the satellite (more or less coinciding with the flight direction). This axis coincides with the axis of drag-free control, which results in a small variance of the signal to be calibrated and thus an inaccurate determination of its scale factor in the presence of relatively large (colored) accelerometer observation errors.
DE: 1200 GEODESY AND GRAVITY
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2007 Fall Meeting