Originally developed to pinpoint attacking aircraft during World War Two, today's advanced radar technology can detect a very different moving target: shifts of the Earth's crust that occur as slowly as the growth of your fingernails.
Radar data from satellites such as ESA's Envisat are used to construct 'interferograms' that show millimetre-scale land movements. These rainbow-hued images provide scientists with new insights into tectonic motion, and an enhanced ability to calculate hazards arising when this slow motion speeds up, in the form of earthquakes or volcanic activity.
The ten-instrument payload on Envisat includes an Advanced Synthetic Aperture Radar (ASAR) instrument designed to acquire radar images of the Earth's surface. Part of Envisat's assigned 'background mission' as it orbits the world every 100 minutes is to prioritise ASAR acquisitions over the seismic belts that cover 15% of the land surface.