Most satellite maps are only two-dimensional. But in the past few years, synthetic-aperture-radar (SAR) images from artificial satellites have been combined into interferograms, to produce high-resolution topographic maps of the Earth's surface and spectacular maps of surface deformation over active faults, volcanoes and glaciers. On page 273 of this issue, Johan Mohr and colleagues present a further improvement of this technique (Mohr, J. J., Reeh, N. & Madsen, S. N. Nature 391, 273–276; 1998).
Instead of mapping only the radar line-of-sight component of ice flow, as in conventional SAR interferometry, they have taken advantage of the differing angles afforded by ascending and descending satellite orbits to map the full three-dimensional flow pattern of Storstrømmen, a large outlet glacier in northeastern Greenland. Above is a perspective view of this flow field looking from the east, with white arrows representing the glacial flow. The slowing near the end of the glacier (left of figure) is unusual, but expected for a glacier that has recently surged. This method can be used to assess the volume changes of land ice masses.