Is that like TERCOM but using strength of gravity rather than terrain height?

Yup, I was just about to comment the same. I find it shocking that there's enough information/variation in gravitational field that you can match on.

	▲	adrian_b a day ago \| parent \| next [-]
		The variation is very small, and that is why it can be exploited only with an extraordinarily sensitive gravimeter, like the one discussed in the article.
	▲	actionfromafar a day ago \| parent \| prev [-]
		Very Star Trek technobabble vibes, except for real!

Precisely.