A spot image of Rutford Ice Stream taken on 8 January 1987, when compared with a Landsat image of 3 February 1974, shows that surface topographic patterns have been displaced down-stream by several kilometres. Ice velocities derived from these measurements agree with those made during limited ground-based surveys in the near vicinity. Earlier interpretation of the surface topography, based on the character of airborne radio echo-sounding records and the relationship between ice thickness and surface elevation (Doake and others, 1987), suggested that there was partial grounding of the glacier sole. If this interpretation is correct, one implication is that the substrate to the ice stream is mobile and being transported at speeds comparable with that of the ice. As this seems unlikely, we are considering alternative explanations.
Radiance values from spot images have been compared with surface slopes measured along an optically levelled line made during a ground-based survey in February 1987. There is a strong correlation between surface slope and radiance, suggesting that our goal of deriving quantitative topographic data from a single satellite image is attainable (Vaughan and others, 1988).