I've read that satellite radar is sensative enough to pick up the 'surface-bulge' caused by a submerged submarine.
I wonder. That would come in handy. The lumpy Earth would also have an influence on the shape of the orbit of the satellite itself, although change in distance is more significant than mass, and measurements from the surface (taking into account the influence of the position of the Moon on both the satellite and the Earth itself) could establish the needed data.