An experimental instrument that combines precision laser spectroscopy and a mobile airborne reflector to map atmospheric gas concentrations could lead to safer methods of detecting hazardous emissions and better modeling of Earth’s atmosphere, its inventors report.
“These measurements are important fundamentally for understanding how gases [mix] and spread in the atmosphere,” said Kevin Cossel, a physical chemist at the National Institute of Standards and Technology (NIST) in Boulder, Colo., and technical lead for the project. “In the future, we also hope to be able to use the system to help detect and quantify hazardous gases,” he added.
To measure gases, the instrument uses a sophisticated type of multifrequency light source, known as a laser comb, to shoot eye-safe lasers through a gas plume at 50,000 slightly different wavelengths simultaneously. The laser sits on an adjustable platform coupled to a telescope. A second component, called a retroreflector, which is a kind of mirror that bounces light back exactly in the direction from which it came, makes it possible to redirect light fired through a portion of the atmosphere straight back to the instrument for analysis.
Until recently, the team had to position the retroreflector by hand on the far side of whatever volume of gas was to be probed, along a line of sight from the laser. Having to set the mirror by hand limited the system to measuring gas concentrations along a single open-air path, Cossel said.
Now, however, the inventors have taken a step that they say makes laser sensing of gas plumes much more versatile. They have mounted the retroreflector on a small remote-controlled drone called a multicopter, which uses helicopter-like propellers to hover and steer. Using a remote control, the scientists can fly the mirror-carrying drone wherever they wish and make it hover to receive a flash of laser light passing through a gas plume at any angle.
With this new mobility, “we’re excited about showing the capability of doing spatial mapping,” said Nathan Newbury, a NIST physicist and the principal investigator for this project. “There’s a lot of interest if we could go vertical to map up to the [atmospheric] boundary layer,” he added.
Ken Davis, professor of atmospheric and climate science at Pennsylvania State University in University Park, expressed his excitement about the possibility of using this system to map “trace gases from sources that are complex in space and time. The mobile reflectors on the copter make that possible.”