The gamma-ray machine operator peers at a screen displaying a medical-film-like image of the first 20-foot container. It shows a dark mass resting atop a more open matrix. He colorizes the image to enhance the contrast. "The dark is dense," he says. "They're saying it's empty wooden boxes, but that density on top is a problem. Density equals mass."
A giant-wheeled front loader called a Port Packer lifts the container off its truck carriage and four burly customs inspectors force it open. Inside, they find that the "empty" wooden pallets have been covered with sheets of plywood. The unreported plywood, most likely filler that was added as an afterthought, was what showed up as density on the operator's monitor.
So far so good, but the inspectors now go to work drilling holes in the wood. They're checking for empty spaces where other sorts of dense materials-drugs or explosives, for instance-could have been hidden. "With inspections like this you don't get much complaint," Baxter says as the battery drills whine. "Now, with furniture shipments . . . " He gives me a smile and shrugs.
Some of the most unusual security efforts in San Francisco Bay are taking place underwater, where a series of shore and dockside instruments and bottom-anchored sensors record the estuary's shifting winds, tides, salinity, and currents, and report the information to shipmasters every 6 minutes over the Web and by dial-up voice mail. Called the Physical Oceanographic Real Time System (PORTS), it was originally a response to one of the worst bridge disasters in U.S. history. In 1980, the freighter Summit Venture, oblivious without real-time information about tides, currents, and winds, rammed into the Skyway bridge in Tampa during a blinding squall, killing 35 people.
The PORTS system has since showed it can mitigate other types of disasters. After a 1996 oil spill in San Francisco, PORTS, which now exists in nine major U.S. waterways, tracked the slick and, through computer models, predicted its trajectory. If terrorists released biochemical agents, radiological weapons, or other toxins into the water, PORTS could potentially track those substances as well. In addition, PORTS data tells Coast Guard officials which parts of the harbor are navigable at any given time. "It doesn't predict where a bad guy may pop up, but it could predict-if someone's coming in a small boat-where they could or couldn't enter the bay and how," says Alan Steinbrugge, director of external operations for the San Francisco Marine Exchange.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.