As the rescue and recovery efforts at the World Trade Center continue, electrotechnology adapted for this purpose is helping to save lives by giving searchers the lay of the land, telling them where it’s safe to tread, and in several instances, standing in for them in places where sending in a human would be unwise or simply impossible.
In the days after the 11 September attack, despite choking plumes of smoke that prevented a visual survey of the wreckage, a twin propeller plane flying 1500 meters above lower Manhattan began making topographic images of the site where the Twin Towers once stood. The plane is equipped with lidar, a laser-based instrument similar to radar that sends pulses of light (instead of radio waves) to a target and measures the time it takes for each beam to be reflected. The device emits 15 000 laser pulses a second, from which EarthData International Inc., Fresno, Calif., the company collecting the data, plots 100 000 points–some as much as 9 meters below street level. The data generated by the lidar system, when combined with information from an on-board global positioning device that tracks the plane’s exact location and altitude, yields topographical information accurate to within 152.4 mm.
The data, collected on an ongoing basis since the attack, has been studied by researchers at the Center for the Analysis and Research of Spatial Information at nearby Hunter College of the City University of New York. The research is being used to produce three-dimensional maps identifying mounds of debris and voids, as well as areas where shifts or collapses are likely to occur.
The lidar-carrying plane has also been outfitted with equipment that measures heat, so rescue teams can track underground fires that continue to smolder and flare up when the debris covering them (and limiting their access to oxygen) is removed.
Also on hand shortly after the attacks were more than a dozen remote-controlled robots that used lights, video cameras, two-way audio, and night vision to give rescue teams an idea of where to search, as well as an up-close glimpse of the obstacles separating them from any survivors. The machines–mostly prototypes financed by the U.S. National Science Foundation, the Office of Naval Research, and the Tactical Mobile Robots program run by the U.S. Department of Defense’s Advanced Research Projects Agency–are designed to traverse the small openings between the steel girders and chunks of concrete in various ways. Some, small enough to fit into sewer pipes less than 305 mm in diameter, can get into even tighter spaces by flattening themselves. Others are adept at standing upright to "see" over obstacles, or using flippers to climb stairs or uneven hills.
The robots range in cost from US $15 000 to $30 000, depending on their sophistication and the number of sensors on board. Many, including the MicroTrac crawler that on 12 September located a pocket of rooms where bodies were later discovered, are customized versions of commercially available machines.
Just as important to the work proceeding at ground zero is the effort to ensure the safety of the people on-site by making sure that neighboring buildings damaged by the collapse of World Trade Center Buildings One, Two, and Seven do not pose a danger. Of particular interest is World Trade Center Building 4, a nine-story structure that engineers from the U.S. Federal Emergency Management Agency (FEMA) noticed was shifting to a degree that suggested it might collapse as well.
To keep a constant eye on its status, FEMA called on James Sabatier, a researcher at the U.S. Army Night Vision Electronic Sensors Directorate’s Laboratory at Fort Belvoir, Va. Sabatier has developed a laser system he hopes will someday accurately detect the presence of landmines by measuring the differences in ground vibrations depending on whether a buried object is present. He quickly adapted this device to measure changes in Building 4’s bearing. Powered by a gasoline generator, the laser system bounces beams off the building’s facade every half second–a technique sensitive enough to keep track of movements on the order of a micrometer. "By this close, constant monitoring, we can let engineers know immediately if there are any big changes in the frequency and amplitude of the oscillation," said Sabatier, who has been working 12-hour shifts monitoring the equipment, which he set up some 46 meters from Building 4.
With a minimum of debate and informed public opinion, the U.S. Congress is considering a number of ways to increase the powers of law enforcement. These include measures that could greatly increase on-line surveillance. Others would redefine many computer-related crimes, such as writing a computer virus, as terrorist acts. This change would potentially expand law enforcement’s authority when investigating such offenses, and increase the penalties for those convicted of them.
The most controversial element in President Bush’s proposal, dubbed the Anti-Terrorism Act of 2001 (ATA), is what the Electronic Privacy Information Center (EPIC), a Washington, D.C.—based cyber-rights advocacy group, calls a significant expansion in "law enforcement authority to use trap-and-trace and pen register devices."
Pen registers and trap-and-trace devices are used to record the phone numbers of calls made by a particular phone. There already is an electronic analog to this: the FBI has asserted the right to capture e-mail header information–to/from addresses and subject lines–and URLs of pages viewed by Web browsers with its so-called Carnivore system, now more innocuously named DCS1000.
DCS1000 is a computer placed on an Internet service provider’s network through which all of its network traffic is routed. Because all traffic is monitored, not just that of an individual suspect, civil rights activists, such as EPIC, argue that DCS1000 already constitutes a questionable expansion of law enforcement’s powers. The ATA would ratify the FBI’s interpretation of these prior statutes that govern trap-and-trace and pen-register—based surveillance.
The FBI argues that e-mail headers and URLs are much like phone numbers--they only indicate whom or what system an Internet user is contacting. Critics point out that e-mail subject lines are more like content than they are like addresses, and that URLs in particular can be quite specific--an Amazon.com URL might list a book’s title or an author’s name, for example. (Reading the content of an e-mail, like listening to an actual telephone conversation, requires a wiretap, for which the authorization requirements are much more stringent.)