| | Exercise 4 - Help, the icebreaker is stuck! - Continued
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|  | Giant tabular iceberg | |
Working with images on the computer
This radar image was acquired on 16 November, 3 days before the icebreaker arrived at Larseman Hills where the Zhong (69-23S 76-22E) and Law Station are situated. On 19 November at 09.00 GMT, the icebreaker reported to be in position 69-11S 75-45E, and remained there, in thick ice, for 6 hours, before continuing its journey from Larseman Hills to Davis Station. On 20 November at 04.00 GMT, the position was 68-45S 77-05E in ice covering only 20% of the sea surface. Some hours later, the ship finally reached Davis Station (68-35S 77-58E).
This image was not available to the ship. If it had been, which way would the captain have gone? Try to find the most convenient track.
| | | Ice floes |
Use LEOWorks to display the file 'ant2003_ex20.tif', which is the radar image taken on 16 November 2003 at 19.03 GMT, and locate the positions indicated above (use View and click Cursor Position/Value). Make use of the Annotation Tool (click the 'A' button) as well to draw your ship track. Improve the contrast of the image using the 'Interactive Stretching'. First click on Enhance. Let us have your result, and we will compare it with the real track and report back to you. This image is geocoded and has a resolution of 375 m.
Download ant2003_ex20.zip (3.1 Mb).
But how can you judge the ice situation from the image?
Study the ice types in the Background chapter of this module.
Here are also some additional hints:
- The dark part close to the land and the glaciers is fast ice. It is a continuous ice sheet of frozen or refrozen seawater. It was formed during the previous winter, and the ice is now rather thick, but icebreakers can penetrate it. In effect, they have to do so in order to reach the research stations. Look out for trails from such ships.
- The very bright points or surfaces are tabular icebergs, mostly with flat tops, broken off from an ice shelf or from glaciers.
Ships avoid them at any cost, as they are very dangerous for shipping (think about the part under water). Huge tabular icebergs can reach the height of 100 m, and tend to break off in pieces.
| | Pancake ice | |
Further north there are a lot of large, mostly dark, ice floes, more or less rounded patches. These are first-year ice, also rather thick. The icebreaker must look for a way to get around them.
The grey area between the large ice floes and elsewhere in the sea represent open water but filled with smaller floes or pieces of ice. These small floes are no problem for icebreakers.
The very small ice floes (pancake ice grease ice), are broken up by wind. The area is bright because of strong winds at the time, roughening the sea.
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