SCIENCE

The study, published in the Nov. 17 issue of Environmental Science & Technology, is based on computer models that indicate the elemental mercury miners used between 1850 and 1900 to capture small grains of gold from sediment has leached into the bay and will persist for decades.

"The good news is the San Francisco Bay is getting cleaner; the bad news is it will take a long time to flush mercury out of the system," Tom McKone, one of the authors, said in a statement. "Our work also demonstrates that we have to live with the messes we make for a long time. It's 150 years since the Gold Rush, and we're still paying for it."

McKone, a staff scientist in the Environmental Energy Technologies Division of the University of California at Berkeley Lab, and his two co-authors, former Berkeley Lab scientist Matthew MacLeod and Donald Mackay at Canada's Trent University, calculated that the various kinds of mercury in the bay are largely responsible for the Bay Area's airborne mercury concentrations. California authorities have issued health advisories about the high level of mercury in fish that swim in the estuary, and scientists suspect that elevated mercury concentrations in local bird eggs may account for their unusually high rate of reproductive failure.

"If we alter the amount of mercury that enters the bay, it doesn't reach a new equilibrium until about 50 years later," McKone said. "We are learning that it takes a long time to clean up the bay."

-- Juliet Eilperin

Pilots May Get Synthetic Vision

Researchers at NASA's Langley Research Center are testing "synthetic vision" systems that would give pilots a continuous three-dimensional image of their surroundings even when they can see nothing outside.

The cockpit display, which is experimental, combines information from global positioning satellite signals with an onboard database to paint a computer-generated picture of the world outside as the plane flies or taxis on a runway.

At night or in clouds or fog, pilots would be able to see a lifelike image showing the plane's orientation and any obstacles, along with guidance information, as if they were looking at a realistic video game.

"When a pilot gets into low-visibility conditions, it's often easy for them to lose their sense of direction due to numerous factors. This situation happens too often and consequently is the leading cause of aircraft accidents," deputy project manager Steven D. Harrah said in a telephone interview. Synthetic vision systems attempt to rectify this situation by supplementing or replacing the pilot's natural vision.

This summer, Langley engineers put the system through several flight tests and demonstrations in Hampton, on board Boeing 757 and DC-8 jets and other general aviation aircraft.

NASA and its corporate partners hope the system can be ready for commercial use in 10 to 15 years.

-- Mike Zimmerman