Fig. 1: Measuring surface movement with InSAR.
From: How satellite InSAR has grown from opportunistic science to routine monitoring over the last decade
An orbiting satellite sends a coherent radar signal to the surface and measures the backscattered radiation. The phase difference (position in the wave cycle) between the signals returning at two different times (time 1 in black and time 2 in red) can be used to estimate ground movement caused by a range of mechanisms.
