Investigation of Methods for Global Gravity Field Recovery from the Dense ERS-1 Geodetic Mission Altimetry

A number of different methods for gravity field prediction from altimetry were investigated in an area of the Greenland-Iceland-Norwegian sea. The investigation was carried out in an area with a relatively small oceanographic signal. The methods investigated were gravity field prediction using inverse Stokes method implemented using FFT and least squares collocation (LSC). The LSC procedure was investigated using different numbers of altimeter data and different procedures. These were gravity field prediction from direct altimetric observations and gravity field prediction using altimeter-derived along-track deflections of the vertical.For the derivation of the global marine gravity field we decided to use inverse Stokes method implemented using FFT as it gives virtually the same result as would have been obtained using LSC directly. However we are missing the associated error-estimates which are obtained using LSC. These may, however, be estimated from the error-estimates obtained in the test area, by scaling the error-estimate using the ration between the local gravity variation and the value in the test area.