Ice flow physical processes derived from the ERS-1 high-resolution map of the Antarctica and Greenland ice sheets

The ERS-1 satellite, launched in 1991, has provided altimetric observations of the Greenland Ice Sheet and 80 per cent of the Antarctica Ice Sheet nor th of 82 degrees S. It was placed in a geodetic (168-day repeat) orbit betw een April 1994 and March 1995, yielding a 1.5 km across-track spacing at la titude 70 degrees with a higher along-track sampling of 350 m. We have anal ysed the waveform altimetric data from this period to compute maps with a 1 /30 degrees grid size. Data processing consists of correcting for environme ntal factors and editing and retracking the waveforms. A further step consi sts of reducing the radial orbit error through crossover analysis and corre cting the slope error to second order. The high-resolution topography of bo th ice sheets reveals numerous details. A kilometre-scale surface roughness running at 45 degrees from the flow direction is the dominant topographic characteristic of both continents. Antarctica also exhibits many scars due to local flow anomalies. Several physical processes can be identified: abru pt transitions from deformation to sliding and vice versa, and impressive s trike-slip phenomena, inducing en echelon folds.