WHEN it comes to fighting forest fires, time is more than money. It's acreage as well.
''Fire growth is a nonlinear function of time,'' said David Martell, a professor of forestry at the University of Toronto who runs a fire management laboratory there. ''If it takes twice as long to find a fire, it will be four times the size when you get there. You definitely want to find it when it's smoldering.''
But finding a fire that is still in its formative stages isn't easy. Satellites only provide an alert after a blaze covers a large enough area to be seen from orbit. Motorists and hikers with cellphones often report small fires, but there are plenty of places that are far from roads or trails.
In their efforts to fight forest fires, the United States Forest Service and other agencies have long used infrared cameras on airplanes. Because of their shortcomings, however, the systems are more commonly used to map the progress of known fires than to discover new ones.
Now Donald McKeown and Michael Richardson, two imaging scientists at the Rochester Institute of Technology, have come up with an airborne array of four digital cameras that they plan to begin testing this summer. They say the array will overcome several significant problems with current aerial camera systems and distinguish fires as small as one foot across from a height of 10,000 feet.
''The Forest Service basically wants to see a smoldering stump,'' Mr. McKeown said.
Although a smoldering tree stump might seem relatively innocuous, it can act as a kind of time-delay fuse to start a major fire. After a lightning strike, the most common cause of forest fires, a stump can smolder harmlessly for days. But if a strong wind comes up, embers can jump to nearby trees or underbrush, causing fire to spread quickly through a forest.
Initially Mr. McKeown and Mr. Richardson, who formerly developed custom imaging systems at Eastman Kodak, looked at the possibility of creating a special high-resolution satellite dedicated to finding forest fires. But they concluded that improving airborne surveillance technology made more sense, at least in the United States.
Mr. Richardson and Mr. McKeown found that current airborne systems have not been significantly upgraded in many years. ''They're using 25-year-old technology,'' said Mr. Richardson.
The biggest problem with current fire-spotting cameras is their tendency to generate false alarms. They use two cameras, each sensitive to different wavelengths of infrared light. But on their operator displays, the infrared radiation created by sunlight reflecting off rocks and water is generally indistinguishable from the radiation generated by a fire.
As a result, firefighters usually wait until nightfall to search forests with those airborne cameras after, say, a major lightning storm.
The key to the new system lies in the relationship between the radiation of energy and wavelengths, discovered by the physicist Max Planck. Basically, Mr. McKeown said, hotter objects emit more radiation in shorter wavelengths, peaking near one end of the infrared portion of the electromagnetic spectrum. Cooler objects emit radiation in longer wavelengths peaking nearer the other end of the infrared portion.
By analyzing the distribution of wavelengths of a particular light source -- a spectral fingerprint, in essence -- a detection system can indicate what kind of source it is. Reflected sunlight, for instance, has more shorter-wavelength light than the flames of a forest fire, Mr. McKeown said.
Because they rely on only two infrared cameras, current systems have difficulty analyzing the distribution of wavelengths from a hot spot. ''If I only sample two points, I won't know if the peak is to the right of the spectrum or the left,'' he said.
The two researchers believe that adding a third infrared camera to the mix will solve the problem. The infrared cameras in their test array chop the spectrum into three parts. Fires, which have values that peak toward the right, or longer-wavelength, end of the spectrum can then be easily distinguished by image analysis software.
The group's camera array can uncover smaller fires largely because the resolution of infrared cameras has greatly improved over the last five years. But that increases the potential for a new kind of false forest-fire alarm: those caused by campfires and other controlled blazes.
To avoid that, the R.I.T. array includes a fourth high-resolution camera that takes conventional pictures in the visible light spectrum. The fire observer who operates the system when it is airborne will only see those images. If the infrared analysis software detects a fire, it will superimpose an icon at its location. The operator can then digitally zoom in on that portion of the picture. ''If I see a tent or picnic tables next to the fire, then I know it's fine,'' Mr. Richardson said.
Because the system can also pinpoint a fire using global positioning system technology as well as a fiber-optic gyroscope (which determines the angle at which the cameras were pointing when they snapped their images), the operator can also precisely direct firefighters to the scene by radio or e-mail.
''If the cost-effectiveness of this technology is good, then it will be a valuable contribution,'' Dr. Martell said. The Rochester researchers estimate that a production version of their camera array, along with its computer system, will cost $500,000 to $750,000.
Before production begins, however, the Rochester Institute of Technology will have a twin-engine plane fly a prototype camera array in July over a series of charcoal fires of precise size in the Rochester area. Mr. Richardson said the students who tend those fires would be responsible for bringing their own hot dogs and marshmallows.
Drawing (Mary Ann Smith)