LYING in his helicopter, Sgt. Frank Sheer of the Orange County Sheriff's Department in Southern California can be literally miles from the action. But that does not mean that he and his co-pilot do not know what's going on. In fact, Sergeant Sheer says they often have a clearer picture of a crime scene than the officers who are there.

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"We'll be tracking a suspect on a hillside from the helicopter," said Sergeant Sheer, the chief pilot in the Orange County force, "and the deputies climbing up it will be saying to us, `There's nobody here.' We've actually had them step on a guy who pulled up a bush for cover."

It's not just having a bird's-eye view that gives Sergeant Sheer and many other airborne police officers, rescue workers, military personnel, and television news and movie crews almost paranormal vision. Nor is it simply advances in optics and cameras. Ultimately they all rely on complex camera stabilization systems that mix mechanical and electronic technologies to produce steady images, even at high magnification, from inherently unsteady craft like helicopters and boats.

When officers pursued O. J. Simpson along the freeways of Los Angeles eight years ago, a covey of police and television news helicopters tracked him with stabilized cameras hanging at the sides in their distinctive ball-shaped pods. But most helicopter surveillance is not that dramatic. If the Orange County Sheriff's Department needs a car discreetly followed, Sergeant Sheer can keep tabs on it from 3,000 feet up and a considerable distance behind — a position that would leave most motorists unaware there was a helicopter around, let alone watching them.

New systems built around all-electronic motion-sensing technologies are so stable that only the horizon and haze limit how far away observers can be.

The use of airborne stabilized cameras to create films or follow athletes in action attracts little controversy. Nor does anyone dispute that the systems allow police officers to capture criminals or rescue people. Some privacy advocates, however, are concerned that the recent proliferation of airborne cameras and the growing capabilities of new systems may mean that anyone who steps outside may unknowingly be a target of an aerial eye. Outdoors, there may no longer be any place to hide.

"Because technology affords police what amounts to superhuman vision, that doesn't mean we lose all expectations of privacy," said Barry Steinhardt, the director of the American Civil Liberties Union's program on technology and liberty. "There are lots of innocent people who are going to have their privacy invaded — observed naked in their backyard sunbathing from far away."

There is a long history of efforts to produce steady airborne pictures. But in the early years, the results were for the most part dismal.

Steven Poster, the president of the American Society of Cinematographers, recalls his first attempt at photography from a helicopter, in the late 1960's. "It was an Illinois State Fair, and the stabilization came from a rope tied around me to the helicopter," Mr. Poster recalled. "I quickly realized that this was not a very good system."

While more sophisticated systems existed back then, they did not differ much from Mr. Poster's rope. Known as side mounts, they generally relied on bungee cords and the user's body to isolate the camera.

By the 1980's Mr. Poster was a director of photography for feature films and television advertisements, and he had found an answer to his aerial photography problems with a system made by Wescam, a company now based in Burlington, Ontario.

"It's the best way to stabilize a camera," said Mr. Poster, who has used the system in films like "Stuart Little 2," which is to be released this summer.

The Wescam system used by Mr. Poster's film crews is remarkably similar to the original Wescam developed in the early 1960's by a Canadian subsidiary of Westinghouse as a battlefield surveillance tool for the Canadian military. (Wescam is short for Westinghouse camera.)

Eliminating the vibration from the helicopter was the first step and the easy part. The Wescam ball is attached to a helicopter or airplane through a shock absorber that uses springs and other damping materials. "It is tuned for the natural frequencies of helicopters," said Mark Chamberlain, a mechanical engineer who is president and chief executive of Wescam.

But eliminating the vibration does nothing to limit three other kinds of movement by the camera: pitch (plunging up and down), yaw (rotating around a vertical axis) and roll (the side-to-side rotation that creates a moving horizon).

To deal with these kinds of movements, inventors of the original Wescam turned to large gyroscopes, which create inertia. It is like strapping a large boulder to the camera to stabilize it, yet without all the weight that a boulder would add.

Inside the camera ball are three gyros oriented to offset each of the three types of unwanted motion. Motors attached to the camera mount allow an operator within the helicopter to view images from the camera on a video monitor and point the camera as needed.

The gyro stabilization system proved so steady that it has not significantly changed over the last three decades. But the system has one significant drawback: the gyros require frequent maintenance.

That is not a problem for the movie industry, which rents the camera systems for short periods. (Other companies, including Gyron Systems International, Tyler Camera Systems and Spacecam Systems, also offer stabilized motion picture cameras.) But the need for maintenance made the systems largely impractical for full-time use by police, the military and television stations.

After Mr. Chamberlain led a management buyout in 1987 of the engineering company that had come to control the Wescam technology, he turned its attention to introducing a technology that was more robust.

Instead of providing stability, its three gyros wobble slightly when the rig changes directions. Sensors measure the wobbling and feed the data to microprocessors that in turn use high-speed electric motors to move the camera and offset the unwanted motion.

The second-generation technology — what Mr. Chamberlain calls a sense-and-react system — has only about half the stability of the original Wescam, so it cannot be used with lenses with very high magnification. But for the Orange County Sheriff's Department, it is unquestionably an improvement over using hand-held binoculars from a helicopter.

"At 1,500 feet we're not reading license plates, but we can tell if it's a man or a woman on the ground," Sergeant Sheer said.

Like many systems used by police forces, one of the two Wescam systems owned by Orange County has a night vision camera that creates images by capturing the infrared radiation emitted by warm objects, including people.

But a United States Supreme Court ruling last June has forced the Orange County Sheriff's Department and other police forces to change the way they use those thermal imaging cameras. The court said that the police could not train thermal imaging cameras on private homes without a warrant.

Mr. Steinhardt of the A.C.L.U. said he would like to see legislators, rather than the courts, come up with specific rules for police use of helicopter camera systems. The A.C.L.U. does not oppose the use of cameras "under the rare circumstance that the police might be legitimately in pursuit of a hot suspect," he said.

"But in the end, that's not how it's going to be used," he added. "It's going to be used in ordinary law enforcement, and that's very different."

It is also being used from ever greater distances. Four years ago Wescam introduced a third stabilization system that combines the reliability of cameras like those used by the Orange County Sheriff's Department while offering even greater stability than the original system. It replaces the spinning mechanical gyroscopes with fiber-optic gyros, which use bursts of laser light to calculate movements by the camera system in each direction.

Once measured, the movement is also offset with a new technology known as magnetic torque motors that can apply a force in a specific direction but allow free movement in all other directions.

Not only is the new system much faster, said Steven Tritchew, Wescam's chief technology officer, but it will also provide a steady image with the magnification of "any lens being made." Practically speaking, atmospheric haze and, ultimately, the impossibility of seeing beyond the horizon are the only limits on how far it can see. "We call it the ground-based Hubbell — we can see a long way," Mr. Chamberlain said.

Certainly Lt. Keith Howland, a mission commander and tactical coordinatorbased at the Naval Air Station in Brunswick, Me., noticed a big difference after an old system in his P-3 Orion surveillance airplane was replaced by a turret with Wescam's new technology about a year ago. "You wouldn't even place them in the same universe," he said.

While on patrol, Lieutenant Howland said, he can watch events on the ground "well outside of visible range."

Like many civilian cameras, the Wescam on the P-3 can be aimed by punching in Global Positioning System coordinates. Software allows it to track moving objects on the ground more or less automatically.

While his aircraft's camera system cannot match the broad sweep of surveillance satellites, Lieutenant Howland said that it had many other advantages. "Basically we can be in real time on a target, see things at the moment they happen, and report it," he said. "It's live video versus a picture."

The systems can be costly, with the most advanced models costing as much as $650,000. But Wescam plans gradually to introduce variations on the new technology into all its markets, potentially giving police departments the same farsightedness. (The Raytheon Company recently introduced a fiber-optic gyro-stabilization system of its own. FLIR Systems of Portland, Ore., is also among the companies that make stabilization systems for police and military use.)

Mr. Chamberlain suggested that the most advanced technology might next go to an even more demanding customer than a police department chasing criminals or a military unit tracking terrorists: the broadcast news industry.

"From a pure image point of view, the military want uninterrupted imagery," he said, "but if it bounces a little bit once in a while or there's a little bit of fuzz on it from interference for a second or two, that's O.K. In the broadcast industry, if it jiggles a little bit or has a bit of fuzz when someone's crossing the finish line, well, you might not get invited back."