Our instruments ( http://www.npl.washington.edu/eotwash/ ) are really good at measuring near-field gravity gradients; we don't build gravimeters at all. We are adapting our gradiometers to make them more field-usable (which might have considerable use in prospecting), but that's not a huge science priority at present. Every few years, we look hard at whether or not we can make a superior mobile gradiometer. If we could, you'd probably know :). We have one new design that might fit into a borehole; if it works well-enough, we may chase commercialization.

A lot of the imaging market appears to come from security/defense applications, either in portal-monitoring or for IED detection. There are defense contractors working on both. The former is easily spoofed (put your uranium pit in a styrofoam sphere in a truck full of grain, done), and the latter is hard to do at speed in a rugged environment.

I've spent a lot of time trying to figure out how to do gravitational imaging on the sub-meter scale, and while it does work, it's hard to get sufficient image resolution to be useful for anything other than a party trick.

If our other science weren't more interesting, I'd be doing it for fun alone. Burning 3-6 months on the project to assess feasibility was as far as I wanted to go without a clear exit strategy.