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Scouting for oil spills under ice.

Oil spilled in the Arctic may become trapped under ice, well out of sight. But Canadian researchers have developed a simple optical system that they now report can identify oil lurking under as much as 1 meter of snow-free ice. This depth limitation should not preclude use of the technique in probing for oil beneath river and lake ice, they report, or first-year ice in the Beaufort Sea and Gulf of St. Lawrence.

When excited by ultraviolet light, electrons in some of oil's ring-shaped aromatic compounds -- such as benzene and especially anthracene - respond by fluorescing, emitting a photon of longer-wavelength light. Though various researchers over the past 20 years have attempted to harness this principle for detecting ice-covered oil, the lasers they employed to deliver the ultraviolet light were never rugged and inexpensive enough to make the concept practical for field use, says Michael E. Moir of Esso Resources Canada Ltd., in Calgary, Alberta.

His team has opted for a simpler system, one that instead irradiates ice with a 10-megawatt flash lamp. By filtering its broadband spectral emissions, they can deliver a microsecond pulse of ultraviolet light that penetrates even cloudy ice.

In lab tests, a photodiode successfully detected the telltale fluorescence from crude oil under ice made from freshwater and synthetic seawater. But when they field tested the technique a month ago in a test basin capped by 16 inches of ice, Moir's team found they could dispense with the photodiode altogether. Even wearing goggles to protect against the lamps intense flash, their eyes easily picked up the fluorescence from plastic bags of oil inserted below the "pretty opaque-looking ice."

Of course, Moir says, having this technology begs the question, "What do you do if you find oil?" After all, he points out, it's still buried, its quantity is unknown, and it might be near-impossible to retrieve.
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Title Annotation:optical system detects oil under Arctic ice
Author:Raloff, Janet
Publication:Science News
Article Type:Brief Article
Date:Apr 24, 1993
Words:308
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