Cross-Overs Assess Quality of GOCE Gradients

We address the important issue of quality assessment of GOCE gravitational gradients. To assess the gradients quality before being used in geophysical research and geodetic applications, a validation method is investigated that compares gradients in satellite track cross-overs (XO). The comparison of two three-dimensional measurements like the GOCE gradient tensors has to be performed in a common coordinate system, which requires tensor rotation. The XO residuals are then analyzed. An anomaly in the \({{\varvec{V}}}_{yy}\) component is identified affecting gradients in vicinity of the geographical and magnetic poles that spread to other tensor components (mainly \({{\varvec{V}}}_{xx}\) and \({{\varvec{V}}}_{xz})\) in the context of tensor rotation. The analysis of all non-anomaly-affected XO residuals underlines the very good quality of the GOCE gravitational gradients: \(\Delta {{\varvec{V}}}_{xx}\) and \(\Delta {{\varvec{V}}}_{yy}\) have an RMS of only 3.2 mE, the RMS of \(\Delta {{\varvec{V}}}_{zz}\) is only slightly worse with 5.3 mE.