Mirrors Help Drone Accurately Measure Airborne Particles
While unmanned aerial vehicles (UAVs), more commonly known as drones, have gained widespread attention in recent years, the use of mirrors on these flying vehicles is not so commonplace.
However, a new drone developed by an Aerospace team led by Dr. Steven Beck, a member of the Electronics and Photonics Lab, Engineering and Technology Group, uses strategically mounted mirrors and Global Positioning System (GPS) receivers to assist with guiding a laser beam to a designated target in the detection and tracking of airborne chemicals.
These chemicals can range from greenhouse gases to industrial airborne effluents.
Traditional laser remote detection systems fire lasers through airborne chemicals of interest and measure the laser light reflected off a naturally occurring obstacle such as a cloud or distant mountain. But, as Beck points out, these traditional systems are limited because scientists cannot control the location or reflectivity of a cloud or any other naturally occurring reflector.
The Aerospace team’s innovative chemical detection and tracking system, known as the Tracking Atmospheric Differential Absorption system, or TADA, also relies on laser-based differential absorption, a remote sensing technology that identifies and measures airborne chemicals by passing laser beams from a transmitter through the air, where they are reflected off of a mirror and then travel back to the transmitter.
According to Beck, analyzing the intensity of the return laser light as the frequency of the laser is tuned across a molecular absorption feature allows the identity and concentration of trace chemicals in the laser path to be measured.
“The innovative aspect of the Aerospace system is that the retro-reflecting mirror is mounted onto a UAV, allowing the mirror and subsequently the measurement path, to be continuously repositioned,” explains Beck. “The laser transmitter must then track the UAV in order to hit the mirror and receive a signal.
“This is a breakthrough approach that gives us the ability to much more accurately measure, and therefore assess, the level of a particular airborne species,” said Beck. “It allows us, for example, to measure and even map elevated targets, such as smoke stack plumes, from the ground. By putting a differential GPS unit on the drone and continuously relaying that position back to the ground-based laser transmitter, we have the ability to point the laser to within one inch of the flying target, and hit the retro-reflecting mirror.”
Working in tandem with the GPS unit is a realtime kinematic (RTK) system to enhance the precision of positioning data derived from the GPS. The same type of RTK systems are used for precision farming to help guide farmers in planting crops and setting up irrigation systems.
The concept was patented by Aerospace about a year ago and has broad application. Ultimately, Beck anticipates that this system will be used for such purposes as seeking out gas leaks from fracking fields. The project is funded under an independent research and development contract by the corporation’s Research and Program Development Office headed by Dr. Randy Villahermosa.
This highly discriminating system enables multidimensional mapping of trace levels of airborne chemical types even in less-than-optimal conditions, Beck said. This groundbreaking approach dramatically improves current capabilities in the tracking of a variety of tiny airborne chemical compounds for an assortment of applications. Using the agility of UAVs to perform chemical monitoring also allows the development of more sophisticated mapping and imaging schemes.
“This airborne particle detection method really affords us the opportunity to target vapors with unparalleled accuracy,” said Beck. “Before incorporating mirrors on the drone, we could achieve only a modicum of accuracy when it came to measuring the degree of a particular airborne species as identified with the laser,” he added.