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Floating iceberg
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Probably the first mention of icebergs was that of St Brendan, an Irish monk whose partly fictional writings suggest that he encountered a "floating crystal castle" on the high seas.
Detection and destruction
In the open ocean most ice is seen by radar at ranges depending on fragment size, but smaller icebergs or growlers (残碎冰山) can be detected only when the sea surface is calm and then only at ranges of about two kilometres.
The reflectivity of ice and snow to light is great, but reflectivity to radar or short radiowaves is very poor. An iceberg seven metres high cannot be detected with modern equipment if the waves are over one metre high.
Sonar (声波定位仪) is effective in detecting icebergs; however, the range of detection is frequently limited by the water conditions and speed of commercial vessels. The likelihood of insufficient warning for high-speed passenger and cargo ships leaves this mode of detection inadequate.
The problem of iceberg protection, therefore, is one of tracking icebergs as they come down the Labrador Current and reporting the whereabouts of these floating menaces to all North Atlantic shipping as often as twice daily.
This sometimes involves 300 icebergs and requires a team of iceberg experts, oceanographers and seamen.
During heavy ice conditions two US coast guard planes fly six-to-eight-hour reconnaissance missions from Argentia, over the Grand Banks off Newfoundland and contiguous (邻近的) areas. When dangerous icebergs approach the shipping lanes, a ship departs for the scene to stand by near the iceberg and warn approaching ships.
Once an iceberg is spotted in a position of threat to ships, it should be of no harm if destroyed. Destroying a 200,000-tonne block of ice is, however, a task whose difficulties leave it impractical in most situations.
The first successful results on breaking up icebergs by explosives were reported in 1929, when a few hundred kilograms of thermite (高热剂) cracked an iceberg into smaller pieces through thermal stress; these then melted rapidly.
Attempts at bombing and torpedoing, however, have been unsuccessful.
(The end)(SD-Agencies)
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