Researchers plan to use a sensor to receive the returning beam and determine what contaminants it encountered on the way back.
"In general, when you want to determine if there are contaminants in the air you need to collect a sample of that air and test it," Miles said. "But with remote sensing you don't need to do that. If there's a bomb buried on the road ahead of you, you'd like to detect it by sampling the surrounding air, much like bomb-sniffing dogs can do, except from far away. That way you're out of the blast zone if it explodes. It's the same thing with hazardous gases you don't want to be there yourself. Greenhouse gases and pollutants are up in the atmosphere, so sampling is difficult."
The most commonly used remote laser-sensing method, LIDAR -- short for light detection and ranging -- measures the scattering of a beam of light as it reflects off a distant object and returns back to a sensor. It is commonly used for measuring the density of clouds and pollution in the air, but can't determine the actual identity of the particles or gases. Variants of this approach can identify contaminants, but are not sensitive enough to detect trace amounts and cannot determine the location of the gases with much accuracy.
The returning beam is thousands of times stronger in the method developed by the Princeton researchers, which should allow them to determine not just how many contaminants are in the air but also the identity and location of those contaminants.
The stronger signal should also allow for detection of much smaller concentrations of airborne contaminants, a particular concern when trying to detect trace amounts of explosive vapors. Any chemical explosive emits various gases depending on its ingredients, but for many explosives the amount of gas is miniscule.
While the researchers are developing the
|Contact: Steven Schultz|
Princeton University, Engineering School