Preprocessing of gravity gradients at the GOCE high-level processing facility |
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Authors: | Johannes Bouman Sietse Rispens Thomas Gruber Radboud Koop Ernst Schrama Pieter Visser Carl Christian Tscherning Martin Veicherts |
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Institution: | 1.SRON Netherlands Institute for Space Research,Utrecht,The Netherlands;2.Delft Institute of Earth Observation and Space Systems (DEOS),Faculty of Aerospace Engineering, Delft University of Technology,Delft,The Netherlands;3.Deutsches Geod?tisches Forschungsinstitut (DGFI),Munich,Germany;4.Institut für Astronomische und Physikalische Geod?sie (IAPG),Technische Universit?t München,Munich,Germany;5.Delft,The Netherlands;6.Niels Bohr Institute,University of Copenhagen,Copenhagen,Denmark |
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Abstract: | 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. |
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Keywords: | GOCE High-level processing facility Gravity gradients Preprocessing Calibration |
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