A satellite the size of a small car can spot the ground beneath it shift by less than the width of a fingernail. Interferometric Synthetic Aperture Radar (InSAR) does this by comparing the phase of microwave echoes recorded on repeat satellite passes; any change in path length shows up as coloured fringes that can be converted into millimetres of motion. Because radar works through cloud and in darkness, the technique delivers truly all-weather ground-deformation maps, turni