Testing frame-transformation, gridding and filtering of GOCE gradiometer data by least-squares collocation using simulated data

Abstract

Least-squares collocation (LSC) has been used to test frame transformation, filtering and gridding of GOCE gradiometer data. Initially the function of the GRAVSOFT program GEOCOL was checked by using noise-free data with 5 s sampling provided by IAG along a 1 month realistic orbit. Data in a 2° x 2° area was used. For these data it was verified that 0.1° frame transformation and gridding in an interior 1°x1° area of one quantity from the same quantity could be done with an error below 5 % of the signal standard deviation. If several components of the gravity gradient were used, the error decreased slightly. Noise with standard deviations of 0.050 and 0.150 Eotvos Units (E=10-9/s2), respectively, and a 1 s correlation distance was generated and added to the data. For the 0.050 E noise the result of the gridding was as for the data without noise, when 1 s sampling was used. For the 0.150 E data, the use of totally 2 months of simulated data and all 3 diagonal components of the gradient matrix were necessary in order to obtain a result below 10 % of the signal standard deviation. Further improvements are possible if data from a larger area or from the planned second measurement phase of GOCE are used.