Mohamed Shams Adoha

It's a pair of satellites that move around the Earth's orbit in kind of every 90 minutes.

And by measuring the distance between the two satellites, you can actually make out how much gravitational field on Earth's surface is changing.

And he says... By knowing the distance, a geodesist can turn that into a field of gravitational anomaly on the Earth's surface.

And the only reason the Earth's gravity will change within a matter of, let's say, a month, is because of movement of water from one place to another, from one season to another.