merican forces seeking the hide- outs of Osama bin Laden are being equipped with sophisticated new technology — an array of sensors — that can pierce darkness, bad weather and as much as 100 feet of solid rock, homing in on heat, magnetic fields, vibrations and other faint cues.
The devices, borne by aircraft, towed behind vehicles or carried by soldiers, can sense slight traces of heat on a cold mountainside, the hum of a buried generator, the magnetic signals from electrical wires.
Some of the sensors did not exist just a decade ago, while others have had their accuracy greatly improved in recent years by the same digital revolution that has drastically increased the power of video recorders and computers. The devices were described by government officials and scientists who spoke on the condition of anonymity because many aspects of the technologies are classified.
The sophisticated surveillance equipment could be particularly valuable, government officials say, now that the fast-moving military campaign in Afghanistan has forced leaders of Al Qaeda and the Taliban to shun radios and mobile phones, which had been routinely intercepted by electronic sensors on American spy planes.
As it happens, the heat-sensing devices will work with increasing efficiency as cold weather tightens its grip in the region. Scientists who helped develop the equipment say the slightest hint of warm air escaping from a tunnel or cave will stand out like a beacon from miles away.
"As it gets colder the caves are going to stay warm," a government scientist said. "Openings that release that air are going to be seen as a hot spot."
Some heat-sensing devices used on American warplanes, unmanned spy planes and scouting vehicles can discern variations in temperature as far as 30 miles away, at a resolution fine enough to reveal a parked vehicle in total darkness.
Lightweight versions of the same kind of device sit atop the gun barrels of rifles and heavy machine guns, allowing marksmen, in dust or darkness, to spot a person a mile and a half away and a car four miles away.
The latest versions not only can detect infrared light emanating from a warm object, but can also decipher details of the chemical composition of the target from telltale wiggles in the emitted spectrum.
Because of great advances in computer power, "we can analyze the atmospherics around something, which helps you know what you are really seeing," said Mike Johnson, a retired rear admiral who is the new president of Recon/Optical, a company based in Barrington, Ill., that makes some of the world's most advanced heat-sensing equipment.
For example, the devices can identify the breath of a soldier or pollutants in the exhaust from a tank.
Scanners developed by the government can detect extremely weak magnetic fields generated by metal equipment stashed in a tunnel up to 100 feet underground. Similar equipment can pick up faint fields from wiring, such as the cables providing lighting to tunnel networks used by Al Qaeda.
Radar that can penetrate the ground and devices that spot underground voids by detecting slight variations in the earth's gravitational field have recently been tested by the Air Force.
This array of target-seeking devices goes far beyond the familiar night-vision goggles, which are standard issue for Special Operations units and the Marines and are probably in the hands of some Al Qaeda fighters because they are widely available in overseas weapons bazaars.
Another value of these technologies is that they can help the military monitor a broad area for hints of activity, and then zoom in for a detailed picture of a potential target.
"The popular conception seems to be that bin Laden and his 40 thieves are in the bottom of some deep cavern, and if we can just find the secret cavern, then the war will be over," said John E. Pike, director of GlobalSecurity.org, a private group whose Web site reports on advances in military technology. "But these guys are undoubtedly scattered all over the place — some in town, some up in the hills, some in houses, others in tunnels."
The sensing methods have been developed as part of a shift by the Defense Department toward locating distant targets quickly, so American forces get the first shot. Using the element of surprise would make it less necessary to harden the defenses for troops in the field, said Dr. A. Fenner Milton, the director of the Army's Night Vision and Electronic Sensors Directorate, in a presentation last year at a conference for military contractors at Fort Belvoir, Va. The goal, he said, is to "substitute information for armor."
For several years, the armed forces have been intensifying the search for ever more sensitive devices. This is what led the Air Force within the last two years to practice by detecting an underground bunker with a gravity-measuring instrument at Vandenberg Air Force Base in California and locating old mines in upstate New York using ground- penetrating radar.
In the meantime, the Marine Corps has been holding informal competitions in which companies show off their latest night vision or thermal imaging systems at its Warfighting Laboratory in Quantico, Va.
Military officials choose participants by scouring conferences held by the fast-growing industry developing surveillance and security technology.
One contestant at this year's session was Aerial Films, a company in Sarasota, Fla., that sells helicopter- mounted camera systems that combine conventional high-resolution video cameras, night vision devices and infrared sensors.
Using a telescopic night vision scope and thermal imaging, company officials consistently spotted marines doing their best to hide in the blackness, said Ken Sanborn, a founder of the company.
"We were reading their names on their uniforms from 500 yards away," he said. "We caught one Marine making cell calls."
