In-flight GOCE Gradiometer Calibration And Validation

One of the key observables of the European Space Agency's Gravity field and steady-state Ocean Circulation Explorer (GOCE) Mission will be the gradiometer measurements. The GOCE gradiometer consists of three pairs of identical ultra-sensitive accelerometers, mounted on three mutually orthogonal arms. To meet the mission goals - determine the Earth's gravity field and its anomalies with an accuracy exceeding 1 mGal, and the global geoid with an accuracy of 1-2 cm at a spatial resolution of 100 km - the calibration and validation of the gradiometer is of utmost importance. The instrument will undergo a series of calibration procedures before launch. In flight, the gradiometer will be calibrated prior to the scientific measurement phases by employing a unique satellite operating mode comprising satellite and proof mass shaking and calibration techniques. Ultimately, the gradiometric measurements are externally calibrated using external gravity information over well- surveyed areas and global gravity field models. In this paper, the calibration schemes and methods are described in detail. It highlights the benefits of using a series of calibration and validation steps. Specific focus will be put on the description of the in-flight calibration and validation part and numerical results using data from the GOCE End-to-End simulator will be presented. The paper concludes with an outlook and a discussion on possible future developments.