Sea-surface height data from satellite altimetry offers itself as avery powerful means of determining the general ocean circulation. Inorder to use it in time-independent problems, one has to use theequipotential height of a geoid model as a reference surface. Up tonow, this reference surface is not known to an accuracy sufficientfor ocean state estimation, as is demonstrated in the context of aninverse analysis of a particular hydrographic section in theSouthern Ocean with altimetry data relative to the geoid height ofthe EGM96 geoid model.