Sea ice observation by means of satellite

For a small area (about 120 km × 150 km) of the Arctic Ocean off the shore of north Alaska the ice conditions were examined in detail by satellite imagery. Instead of using 64 steps of gray, 15 brightness steps were distinguished by computer for each data point. To suppress the transient cloudiness, minimum brightness composites were used. The ice conditions could be drafted in great detail for 5-day periods for the summer of 1969, this fact showing the value of satellites as a unique tool for sea ice reconnaissance. The ice conditions were found to depend strongly on the wind direction. Offshore wind moved the ice out, and wind toward the shore brought it back. A good correlation was found with the wind taken from the weather maps, although the data from a ground-based climatological station were not always in good agreement with the ice movement, probably because of orographic effects. A comparison with ice charts mapped by more conventional methods showed good agreement in most cases. The satellite picture, however, gave much greater detail. Monthly mean albedo maps were constructed from the brightness composites for the 4 months from mid-May to mid-September and compared with previous measurements.