It is shown, by random construction of many sea surfaces, each consistent with geostrophy and mass conservation in the underlying ocean, that absolute sea surface topography relative to a geopotential surface can be estimated to 10 cm accuracy from appropriate in situ measurements of density....
Roemmich, Dean, and Carl Wunsch. 1982. "On combining satellite altimetry with hydrographic data." Journal of Marine Research 40, (S). https://elischolar.library.yale.edu/journal_of_marine_research/1659