InSAR (Interferometric SAR)

Comparing the phase of two SAR images of the same place taken at different times to measure ground movement down to millimeters.

Why it matters

InSAR detects subsidence, earthquakes, volcano inflation, glacier flow, and infrastructure shifts — movements far too small for optical satellites to see.

Where you’ll meet it

• InSAR runs on the same radar data as SAR — typically Sentinel-1 image pairs, which are free and have a steady repeat schedule perfect for tracking change.
• NISAR (the NASA–ISRO mission) was designed largely for InSAR, mapping how Earth’s surface deforms from earthquakes, volcanoes, and sinking groundwater basins.
• NASA’s ARIA project turns Sentinel-1 InSAR into ready-made deformation maps after major earthquakes — a finished product rather than raw phase data.

In plain terms

Like overlaying two photos of a face and measuring how much a wrinkle deepened — the tiny difference is the signal.