What would you do with the g measurement to get your location? Can g deltas be matched to sea floor contour maps? Otherwise it seems like subs would have to be following g-mapped routes.
With a highly detailed map, it becomes a statistical fitting problem, to locate yourself based on an estimate of position history using intertidal measurements and your time history of gravitational measurements, starting from an initial position estimate. I would imagine this could be quite accurate.
A typical sub drifts by only a few tens of meters per day - obviously this builds up . The point of the BEC gravity map is to reduce this inaccuracy an order of magnitude, thereby extending the subsurface range of the subs.
By having a base map of the gravity of the ocean floor. Picture a contour map, but for values of g.
Same as if you were navigating based on a physical contour map of the ocean floor, except that getting an accurate depth like that in deep waters isn’t possible, and in shallow waters requires sonar.
I'd assume features below the sea floor have a much bigger impact than surface features. Large iron deposits, volcanic activity, natural gas deposits, whatever the LLSVPs are, etc. But you could use ships to correlate gravity measurements with GPS locations and make an accurate map that way. You don't need to map the entire ocean, just enough locations to allow subs to occasionally recalibrate their position.
