Indeed, an early test in March 2001 showed just how independent the devices could be. At a military base in Twentynine Palms, Calif., Pister and his team dropped six motes from an airplane along a road. As soon as they hit the ground, they organized themselves into a network and began sensing the magnetic field around them. When that changed as a vehicle drove by, the motes cooperated to calculate its speed and direction, later transmitting the data to a laptop at a nearby base camp.
Now, several companies make prototypes with customized sensors that are showing great promise in field tests. For instance, last year UC-Berkeley biologist Todd Dawson deployed 80 motes made by Intel to measure sunlight, temperature, and humidity in a half-dozen redwood trees in the campus botanical garden. In addition to eliminating miles of wiring and reducing the cost of his experiments 10-fold, the motes will give him his first 3-D view of the redwood forest microclimate. This month Dawson will pack up his motes and move them to a remote natural grove. His goal is to better understand how the loss and fragmentation of redwood forests affect local climate and water resources. In an even more ambitious study of ecosystems, UCLA's CENS is setting up a network with a couple hundred devices in a forested 30-acre reserve near Palm Springs.
Motes are poised to become practical tools for protecting and managing all sorts of resources. For instance, CENS will test motes to monitor an alfalfa field to see how well the plants dissipate high-nitrate wastewater. Last fall, a vineyard in British Columbia deployed a network of 65 motes to closely track temperature fluctuations on its slopes. One aim is to determine when temperatures are perfect for picking grapes to make a late-harvest wine known as ice wine.
Overload. While the applications of wireless sensor networks seem endless, the first field tests have revealed shortcomings, which companies are working hard to address. Generally, the motes have needed more-robust packaging to survive rough treatment, curious animals, and frigid weather. At times the radios have been as fickle as cellphones in their signaling and reception.
Still, the biggest challenge may be dealing with the crushing load of information smart dust collects. With his redwood project, Dawson says he feels as if he is connected to the New York Stock Exchange. "The data stream that comes in is wonderful," he says, but "absolutely overwhelming." Feng Zhao, manager of the Embedded Collaborative Computing Area at the Palo Alto Research Center in California, is trying to reduce the volume of incoming data by training the motes to pay attention only to what's important in the surrounding environment. Others are trying to ensure that the data are accurate and secure--a crucial step, if motes are ever to be used for, say, monitoring a city for signs of bioterrorism.
As motes are deployed more and more widely, the potential for the misuse of the information they collect can only grow, Culler says. He and his colleagues at Berkeley's Center for Information Technology Research in the Interest of Society are already looking at how laws might be updated to protect the privacy of individuals whose comings and goings, for instance, may one day be tracked by motes. Says Culler, "I don't think it will be difficult to draw the lines, but we do need to ask, `How far do we let this go?' " It's a question far removed from observing seabirds on a wind-swept island.