Tests starting this week in Denver will help scientists
determine if sound can be used to detect, track and predict
hazards from aircraft wake turbulence.

Researchers, including some from NASA’s Langley Research
Center (LaRC) in Hampton, Va., will spend more than three
weeks collecting acoustic data at Denver International
Airport. They will be using precisely calibrated microphone
arrays to measure sound generated by airplane wake vortices.
Two laser radars (lidars) will record the actual position,
track, and vortex strength, so scientists and engineers can
look for subtle characteristics within the wake acoustic

“The purpose of the test is to acquire the best data ever
collected on the wake acoustic phenomena,” said Wayne Bryant,
LaRC Wake Vortex Projects Manager. “We hope to establish
whether an acoustic-based wake vortex sensor is operationally
feasible for the airport environment. One of the key items we
will be looking for is a relationship between the recorded
acoustic signal and the hazard the wake represents. Estimates
of this hazard level will be provided by the lidar systems in
our test,” he said.

Aircraft produce wake vortices when they fly, much like two
small horizontal tornadoes trailing behind the wing tips.
Larger, heavier aircraft produce stronger wakes. Small
aircraft following larger ones can encounter a wake vortex,
if they are too close. Turbulence can be severe enough to
cause a plane to crash.

Wake vortex detectors, such as lidar or possibly a wake
acoustic sensor, are envisioned as important parts of a Wake
Vortex Avoidance System. Such a system may be able to give
pilots advance warning of the location and nature of
hazardous wake turbulence.

The technology could also increase runway capacity, because
air traffic controllers would have a better idea where wakes
are and how they decay. Controllers could use that
information to efficiently separate aircraft.

The Denver test will also provide an opportunity to evaluate
recent modifications to a laser-based wake acoustic sensor
being developed by Flight Safety Technologies and Lockheed-
Martin. The Sensors for Characterizing Ring-eddy Atmospheric
Turbulence Emanating Sound (SOCRATES), projects low power
laser beams across open space onto a reflector device, which
reflects the beams back to a receiver. Developers say the
system then measures the changes in the laser beams, which
reveal the existence of sound.

Participants in the wake acoustics test include NASA; the
Department of Transportation Volpe National Transportation
Systems Center; OptiNav/Microstar/Titan, Coherent
Technologies, Inc.; MIT Lincoln Laboratories; United
Airlines; Florida Atlantic University; Flight Safety
Technologies; Lockheed-Martin; and the German Aerospace
Research Center.

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