Performance Analysis of Goce Gradiometer Measurements

Since the launch of the GOCE satellite on March 17th 2009, a large amount of observation has been collected and needs to be analyzed. Of highest priority are the gradiometer measurements. Gravitational gradiometry measured in a satellite is new and many lessons are to be learnt before one can turn to a global gravity field analysis. Of highest priority is an analysis of the performance of (1) all six three-axis accelerometers, individually, (2) the three gradiometer arms, (3) the separation of the rotational signal from the gravitational one and, finally, (4) the complete three axis instrument. We compared a small set of original GOCE measurements with reference values from the EGM08 gravity field model up to a comparable spherical harmonic degree and order. The gradiometer reaches its highest performance in the so-called measurement band width (MBW) between 5·10 and 0.1Hz with a 1/f increase at lower frequencies. An ideal check of the overall noise behavior is derived from the trace of the gradient tensor, i.e. from the sum of the three diagonal terms of the gradiometer. It serves not only as a diagnosis tool of the gradients but also of possible influences of the measured angular velocities. In addition to these tests some experiments were carried out with various combinations of the individual accelerometer read-outs and of gradiometer components.