Colleagues rallied to look for the renowned computer scientist, but to no avail.
A MOVING TARGET
There were many obstacles. Real-time satellite data isn't available without special government clearance, so the searchers were forced to use ocean images that were delayed by 24 hours. By the time they could work with it, the data would be two days old. Winds, tides, and currents would have moved Gray's boat even if they spotted it. "I decided I'd organize a group that would predict where an object would drift in that period," Bellingham says.
Antonio Baptista at Oregon Health and Science University and Yi Chao at NASA's Jet Propulsion Lab, both experienced ocean surface modelers, tried to predict where a boat located somewhere between the coast and the Farallons might have drifted over several days. Working with different data sets, they came to a similar conclusion: If the boat had come to harm between the coast and islands, it would have been carried back toward shore somewhere north of San Francisco near Drake's Bay.
Olson rallied volunteers and served as an unofficial spokesman
The models also showed that if Gray had for some reason sailed past the Farallons out to sea, Tenacious would still be heading west--winds were offshore at the time, contrary to their usual pattern. Bellingham climbed aboard a Beechcraft Bonanza, a single-engine plane, and served as spotter as civilian pilot Scott Wedge flew up and down the coast. They found nothing. If Tenacious had washed up along the shore, Bellingham says, "at 1,300 feet, we would have seen it."
On Feb. 1, the first data available gave the group a look at patches of ocean south of San Francisco. It came from a NASA pilot flying a civilian version of the U2 spy plane, the ER2, which took off from Moffett Field and flew up and down the coast, its camera eye periodically collecting data. David Tennenhouse, a former manager of Amazon's A9 product search site, funneled the ER2 data into Amazon's storage service, where it was divvied into pieces by Mechanical Turk, experimental software that lets many people work on a task simultaneously.
Images that were 8,000-by-8,000 pixels in size were parsed into 400-by-400 "tiles" that were enlarged so volunteers could examine them for objects. Mechanical Turk automatically handled the distribution over the Web. Each tile was viewed and rated by three volunteers, and only those that got a high rating from all three would move to a second stage of review.
Even so, it was a mind-boggling task. There were 560,000 tiles, requiring 1.68 million viewings. A single tile consisted of 160,000 pixels of monochromatic gray; Gray's 40-foot, red-hulled boat would appear as a mere 6 to 8 pixels with a slightly darker gray tone. "There were more boats in the water than just Jim's," Vogel says. "It was hard to determine with any certainty which might have been Tenacious."
Nevertheless, word of the effort spread, and the task was completed in three days by 12,000 volunteers. Tennenhouse, in charge of coordinating the image data search, groaned at the prospect of thousands of people viewing the ER2 flight data via Mechanical Turk. But the volunteers had examples of what to look for, and some became skilled at distinguishing between a discoloration representing a wave pattern and one representing an object in the water. When a boat was detected, some tried to determine whether a wake could be seen behind it. (A wake indicated a boat under way as intended; they were looking for one adrift.)
At first, the volunteers wanted to identify every object down to the size of a dinghy, in case Gray had to take to the sea after Tenacious sank. But the resolution of the flight data wasn't good enough to pick out a dinghy without thousands of false hits. Tennenhouse insisted that the focus stay on a 40-foot boat.
At that point, Gray had been missing for nearly 10 days. If he was in a dinghy, his survival prospects were poor to nil, given the cold ocean temperatures and lack of fresh water. If he was still on the sailboat, his chances were much better. "We had to throw away some targets. A dinghy couldn't really be distinguished from noise," Tennenhouse says. "My team had to focus on positive outcomes."
As Mechanical Turk turned up targets, called "possibles," Gray's Microsoft Research colleague Tom Barclay was arranging flights by civilian pilots to go check them out. Sending pilots with a spotter 70 miles offshore was itself a risk, so decisions on what to pursue weren't made lightly. As 15 to 20 possibles accumulated, Navy image analysis experts helped determine what they might be. Locations were plotted using the drift trajectories developed by Bellingham's group.
"The Pacific Ocean is a very big place," says Barclay, who worked with Gray in the development of TerraServer, a database of satellite earth images. "Obvious, I know, but it is really hammered home when you try to 'mow it' with low-flying, fairly slow aircraft."
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