Accuracy Analysis of External Reference Data for GOCE Evaluation in Space and Frequency Domain

With the upcoming Esa satellite mission Goce, all components of the gravitational tensor (2nd derivatives of the Earth’s gravitational potential) will be measured globally except of the polar gaps. The highest accuracy level within the measurement bandwidth (Mbw, 5–100 mHz) is 11 mE/√Hz for the diagonal components of the tensor (1 mE = 10-121/s^2). To meet this accuracy level, the gradiometer will be calibrated and evaluated internally as well as externally. One strategy of an external evaluation includes the use of a global geopotential model in combination with ground gravity data upward continued to satellite altitudeIn this study an error estimation for the external reference data is carried out (a) statistically by applying least-squares collocation and (b) empirically in a synthetic environment including (correlated and uncorrelated) noise. The use of synthetic data permits a closed-loop validation in all points. The spectral combination method based on integral formulas with a modified kernel function is applied to compute all components of the tensor. The closed-loop differences are analysed in the space and in the frequency domain. The dependency of the prediction error on the characteristics of the input data (noise level, area size and resolution) is shown. An accuracy below the required level of 11 mE/√Hz can be reached combining gravity anomalies with a noise level of 1 mGal and current global geopotential models