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Calibri 83ffff̙̙3f3fff3f3f33333f33333.?TU Delft Repositoryg 6uuidrepository linktitleauthorcontributorpublication yearabstract
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departmentresearch group programmeprojectcoordinates)uuid:a5ef3998-65f4-40b8-a6d0-31d9dd954729Dhttp://resolver.tudelft.nl/uuid:a5ef3998-65f4-40b8-a6d0-31d9dd954729QUsing the GOCE star trackers for validating the calibration of its accelerometers:Visser, P.N.A.M. (TU Delft Astrodynamics & Space Missions)>A method for validating the calibration parameters of the six accelerometers on board the Gravity field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations that was originally tested by an end-to-end simulation, has been updated and applied to real data from GOCE. It is shown that the method provides estimates of scale factors for all three axes of the six GOCE accelerometers that are consistent at a level significantly better than 0.01 compared to the a priori calibrated value of 1. In addition, relative accelerometer biases and drift terms were estimated consistent with values obtained by precise orbit determination, where the first GOCE accelerometer served as reference. The calibration results clearly reveal the different behavior of the sensitive and less-sensitive accelerometer axes.[Accelerometer; Bias; Bias drift; Calibration; GOCE; Gradiometer; Scale factor; Star trackerenjournal articleAstrodynamics & Space Missions)uuid:22b90d92-9e63-4fa0-8d6e-2106912e23f9Dhttp://resolver.tudelft.nl/uuid:22b90d92-9e63-4fa0-8d6e-2106912e23f9MPreprocessing of gravity gradients at the GOCE high-level processing facilitygBouman, J.; Rispens, S.; Gruber, T.; Koop, R.; Schrama, E.; Visser, P.; Tscherning, C.C.; Veicherts, M.One of the products derived from the gravity field and steady-state ocean circulation explorer (GOCE) observations are the gravity gradients. These gravity gradients are provided in the gradiometer reference frame (GRF) and are calibrated in-flight using satellite shaking and star sensor data. To use these gravity gradients for application in Earth scienes and gravity field analysis, additional preprocessing needs to be done, including corrections for temporal gravity field signals to isolate the static gravity field part, screening for outliers, calibration by comparison with existing external gravity field information and error assessment. The temporal gravity gradient corrections consist of tidal and nontidal corrections. These are all generally below the gravity gradient error level, which is predicted to show a 1/f behaviour for low frequencies. In the outlier detection, the 1/f error is compensated for by subtracting a local median from the data, while the data error is assessed using the median absolute deviation. The local median acts as a high-pass filter and it is robust as is the median absolute deviation. Three different methods have been implemented for the calibration of the gravity gradients. All three methods use a high-pass filter to compensate for the 1/f gravity gradient error. The baseline method uses state-of-the-art global gravity field models and the most accurate results are obtained if star sensor misalignments are estimated along with the calibration parameters. A second calibration method uses GOCE GPS data to estimate a low-degree gravity field model as well as gravity gradient scale factors. Both methods allow to estimate gravity gradient scale factors down to the 10?3 level. The third calibration method uses high accurate terrestrial gravity data in selected regions to validate the gravity gradient scale factors, focussing on the measurement band. Gravity gradient scale factors may be estimated down to the 10?2 level with this method.SGOCE; High-level processing facility; Gravity gradients; Preprocessing; CalibrationSpringerAerospace Engineering<Delft Institute of Earth Observation and Space Systems, DEOS)uuid:7acff12c-4ee9-4c4b-96fc-870948e12224Dhttp://resolver.tudelft.nl/uuid:7acff12c-4ee9-4c4b-96fc-870948e12224|GOCE gradiom<eter: Estimation of biases and scale factors of all six individual accelerometers by precise orbit determinationVisser, P.N.A.M.@A method has been implemented and tested for estimating bias and scale factor parameters for all six individual accelerometers that will fly on-board of GOCE and together form the so-called gradiometer. The method is based on inclusion of the individual accelerometer observations in precise orbit determinations, opposed to the baseline method where so-called common-mode accelerometer observations are used. The method was tested using simulated data from a detailed GOCE system simulator. It was found that the observations taken by individual accelerometers need to be corrected for (1) local satellite gravity gradient (SGG), and (2) rotational terms caused by centrifugal and angular accelerations, due to the fact that they are not located in the satellite s center of mass. For these corrections, use is made of a reference gravity field model. In addition, the rotational terms are derived from on-board star tracker observations. With a perfect a priori gravity field model and with the estimation of not only accelerometer biases but also accelerometer drifts, scale factors can be determined with an accuracy and stability 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) for which the scale factor estimates are unreliable. 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. In the presence of gravity field model errors, it was found that still an accuracy and stability of about 0.015 can be obtained for the accelerometer scale factors by simultaneously estimating empirical accelerations.sAccelerometer; Accelerometer drift; Bias; Calibration; GOCE; Gradiometer; Precise orbit determination; Scale factor)uuid:db473be3-7bca-4e55-aacd-f46954d62c31Dhttp://resolver.tudelft.nl/uuid:db473be3-7bca-4e55-aacd-f46954d62c31kExploring the possibilities for star-tracker assisted calibration of the six individual GOCE accelerometers=A method has been developed and tested for estimating calibration parameters for the six accelerometers on board the Gravity field and steady-state Ocean Circulation Explorer (GOCE) from star tracker observations. These six accelerometers are part of the gradiometer, which is the prime instrument on board GOCE. It will be shown that by taking appropriate combinations of observations collected by the accelerometers, by modeling acceleration terms caused by gravity gradients from an a priori low-degree spherical harmonic expansion, and by modeling rotational acceleration terms derived from star-tracker observations, scale factors of each of the accelerometers can be estimated for each axis. Simulated observations from a so-called end-to-end simulator were used to test the method. This end-to-end simulator includes a detailed model of the GOCE satellite, its instruments and instrument errors, and its environment. Results of the tests indicate that scale factors of all six accelerometers can be determined with an accuracy of around 0.01 for all components on a daily basis.\GOCE; Gradiometer; Accelerometers; Star-tracker; Calibration; Bias; Bias drift; Scale factor#Earth Observation and Space Systems
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