Determination of surface features on glaciers in Alaska from ERS-1 SAR observations

Satellite microwave remote sensing using the European Research Satellite 1 (ERS-1) synthetic aperture radar (SAR) observations enables glaciers to be monitored worldwide. To interpret the SAR observations in the context of climate change, the relationship between radar reflectivity and snow/ice conditions has been extensively studied. In addition, the local surface roughness (microtopography) affects the radar reflectivity. In this study, USGS air photos (1 m resolution) of Columbia and Bering glaciers are used as 'ground truth' to show how surface roughness affects ERS-1 radar reflectivity on sub-resolution spatial scales from 1-30 m. As expected, radar reflectivity is found to increase with increasing surface roughness. Crevasse pattern visibility is strongly dependent on illumination direction in both air photos and ERS-1 data. Crevasse patterns are most visible on ERS-1 when the crevasses are aligned normal to the radar look direction. Therefore, ERS-1 glacier monitoring data is most easily interpreted when collected from a constant look direction. Topographic effects can then be removed from snow/ice state reflectivity differences that determine the position of the firn or equilibrium line. During periods of uniform surface conditions, changes in radar reflectivity may indicate changes in surface topography due to surging.<
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