NASA’s Infrasound Microphone Detects “Clear-Air” Turbulence Hundreds of Miles Away
NASA's infrasound microphone allows pilots and air traffic control to identify aircraft wake vortices, clear air turbulence, and tornadoes hundreds of miles away.
When planning a flight, operators must ensure that an aircraft has the right amount of fuel and a clear path through air traffic. "Clear-air turbulence," or turbulence without visual cues like clouds, can disrupt an otherwise smooth flight and in extreme cases may be detrimental to an aircraft.
Recently, NASA engineers rerouted aeronautical research for use in commercial flight planning with sensor technology that allows pilots and air traffic controls to identify aircraft wake vortices, transparent air turbulence, and tornadoes hundreds of miles away.
A high-level depiction of one way NASA has detected clear-air turbulence in the past. Image used courtesy of NASA
Specifically, two NASA engineers have used their expertise in instrumentation to design an infrasound microphone that will be able to detect high-turbulent areas in the sky.
The Initial Concept of NASA's Infrasound Microphone
In 2007, NASA engineers Qamar Shams and Allan Zuckerwar from NASA's Langley Research Center in Hampton, Virginia designed a solution for air control to detect areas of anticipated turbulence during flight planning.
After initial testing, the engineers quickly discovered that microphones would not work due to a large amount of interference. This harmonic situation wouldn't allow anyone to hear low-end frequencies.
Frequencies that range as low as 0.001 to 20 Hz can be reached through infrasound-based designs. As such, Shams and Zuckerwar began to design a microphone inspired by perceived infrared light (frequencies we can't visibly see) and infrasound.
The ultra-low infrasound microphone is built with a low diaphragm tension and a large-diaphragm radius to achieve low bandwidth and high responsiveness. Image used courtesy of NASA
By 2017, Shams and Zuckerwar received recognition for their infrasound design, winning NASA's Commerical Invention of the Year award. The microphone has been tested at ground level in a triangular arrangement along a runway and was able to pick up high-turbulent sounds 300 miles away.
After this recognition, Stratodynamics Aviation, a company specializing in designing unmanned aerial vehicles (UAV) for high-altitude flight services, saw the potential for adapting this infrasound microphone into an in-flight turbulence detection sensor.
Infrasound Microphone Design and Functionality
To adapt the infrasound microphone into an in-flight turbulence detection sensor, it was first necessary to design an infrasound system. According to NASA's initial publication on the infrasound microphone, the system is composed of an electret condenser microphone, a windscreen, a high-impedance preamplifier, and a signal processing device to collect data.
The electret condenser microphone utilizes an electrostatic capacitor that helps block out unwanted noise. The windscreen also plays a pivotal role since it has a specific acoustic impedance that prevents ambient wind from reaching the microphone, all while letting infrasounds below 0.1 Hz pass through. Couple this with a preamplifier and the results show an isolated low frequency with no effect of ambient conditions.
The Infrasound Microphone Goes Commercial
Qamar Shams assisted Stratodynamics as it continued with the next phase of the infrasound microphone by implementing it into a UAV called the HiDRON. This vehicle can reach a height of 100,000 ft, traveling with an infrasound microphone and a wind probe.
An image of (a) the various sensor packages in the HiDRON's fuselage and (b) an aerial view of the HiDRON UAV. Image used courtesy of Sensors special issue, Application of Unmanned Aircraft Systems for Atmospheric Science [CC BY 4.0]
Nick Craine, the business development lead at Stratodynamics, states, “As infrasonic detection continues to prove its value as a turbulence mitigation technology, it has the potential to forever alter the landscape of aviation, growing stronger with every flight.”
Normally significant amounts of fuel are lost when flights must reroute to navigate around turbulent air. By implementing infrasound technology, this microphone may provide turbulence detection for efficient, cost-effective aviation route planning.
With the potential adaptation possibilities of infrasound technology, the sky will certainly not be the limit.