Borderline bonkers - it's DARPA
Airborne gravity surveys are pretty routine in the oil and gas industry, so it is possible to build gravimeters that can survey being buffeted in a plane and compensate for any movements relative to the terrain.
BUT the differences they're looking to identify here are insanely small - in the tenths or even thousands of a milliGal (i.e. not-a-lot). This sounds only borderline doable, so they'd better turn their beanie-caps up to 11.