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Quick Validation of GOCE Gradients

Focke Jarecki(1), Karen Insa Wolf(1) and Jürgen Müller(1)

(1) University of Hanover, Schneiderberg 50, 30167 Hannover, Germany

Abstract

Contributing to ESA's calibration and validation activities (Cal/Val Team) for the GOCE mission, this paper presents two quick validation methods for GOCE gradients: a cross-over procedure for an internal quality check and the comparison with external reference data in the time and frequency domain.

The cross-over approach includes adequate reduction procedures to deal with altitude and attitude differences for the immediate comparison of the gradient tensor components in satellite track cross-over points. Simulated gravity gradiometry data sets based on different error assumptions are processed. The cross-over validation, as a relative approach, proves to be capable to detect gross errors, data gaps and long term drift parameters well, whereas geographically fixed error phenomena and constant biases remain undiscovered. Combining selected data from different epochs, drift behaviour and short-term biases are very well identified through cross-over validation.

The second part of the paper deals with the computation of external reference gradients with sufficient accuracy in the measurement bandwidth of the gradiometer. Therefore geopotential models are combined with terrestrial gravity and terrain data to improve the high frequency information of the upward continued gradients. Pre-calculated reference gradients from high quality data over Europe are produced. Beyond this, the errors of the computed gradients are studied based on closed-loop calculations with synthetic data including noise and on statistical error estimations. The propagated errors of the upward continued gradients are shown in time and frequency space to evaluate the quality of the gradients in the measurement bandwidth of the GOCE gradiometer.

Dealing just with subsets of the original SGG measurements both methods offer the opportunity to do a quick validation, already on the Level-1B data processing step.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry