They have proposed making gravity measurements at varying levels in the ocean, where it should be possible to avoid most potential distortions from rock.
More recent missions use laser altimetry and gravity measurements instead of pressure to define elevation on Mars.
So from the gravity measurements used to determine a "loss" in mass, I would be curious if they corrected for density?
The first gravity measurements at sea had been made in 1926 from a submarine of the Royal Navy.
Scientists recently reported gravity measurements showing that Europa's ice and water shell apparently reaches down 60 to 120 miles.
Goal: Aerobraking to circular orbit and global gravity measurements.
For example, gravity measurements are used to obtain a model of the density profile under the surface.
The elevation of the point where each gravity measurement was taken must be reduced to a reference datum to compare the whole profile.
They were nonreversible, so it was used for relative gravity measurements, but their small size made them small and portable.
In past decades, Finnish scientists have conducted worldwide ultra-sensitive gravity measurements.