Outlet glaciers-which serve to drain ice from ice sheets-seem to be dynamically less stable in North Greenland than in South Greenland(1-3). Storstrommen, a large outlet glacier in northeastern Greenland which surged between 1978 and 1984 (ref. 2), has been well studied. In general, neither glacier surge mechanisms nor the geographical distribution of the surges are well known. Conventional satellite radar interferometry can provide large-scale topography models with high resolution(4), and can measure the radar line-of-sight component of ice-flow vector(5), but cannot map full vector flow fields, Here we present an interferometry method that combines observations from descending and ascending satellite orbits which, assuming ice flow parallel to the topographic surface, allows us to use the differing view angles to estimate full three-dimensional surface flow patterns, The accuracy of our technique is confirmed by the good agreement between our radar-based now model and in situ Global Positioning System (GPS) reference data at Storstrommen, Radar measurements such as these, made regularly and at high spatial density, have the potential to substantially enhance our understanding of glacier dynamics and ice-sheet flow, as well as improve the accuracy of glacier mass-balance estimates.