National Geographic : 1968 Jun
As a detector of ice, radar does not work as well from a ship as it does from an airplane. In 1959 a freighter was damaged after hitting a growler in the North Atlantic. The skipper later testified that he had read the radar screen faithfully every 10 minutes. Even that was not often enough. Marine radar can detect a menacing "growler" some 8,000 yards away. When it is closer than 3,500 yards, however, reflections from choppy seas and spray often obscure the warning signal. Thus, for safety, a small, low-lying berg must be spotted within the intervening 4,500 yards. At 15 knots, a ship can cover that distance in nine minutes. "There are seamen who cling to the myth that they can detect the nearness of icebergs by taking water temperatures," a Coast Guard oceanographer told me. "Icebergs do not make the water around them colder. When a sudden lowering of the water's temperature is de tected, it usually means that the vessel has moved into the Labrador Current." In the face of so many uncertainties, it is no wonder that ship captains pay careful atten tion to the staccato voice of Station NIK. "Try Not to Hit Us" After accompanying the crew of the Her cules on one dye-bombing mission, I went aboard the Evergreen and saw another. We were at sea for three days before encountering an iceberg judged suitable for marking. The highest and slenderest of the berg's three KODACHROMES BYJAMESR. HOLLAND(C) N.G.S . Satellite photographs taken more than 850 miles up help an oceanographer at Ice Patrol headquarters on Governors Island, New York, determine the extent of pack ice surrounding Greenland. But satellite sensing techniques need refining before such sur veys from space can distinguish with cer tainty between ice and clouds. Prison of ice: A ship crosses the harbor of St. John's, Newfoundland, through a chill ing white mosaic. Soon heavier ice moved in, closing the port in the spring of 1967 for the first time in two years.