NASA, NCAR use LIDAR to measure clear air turbulence

BROOMFIELD, Colo. - A combination of conventional radar and the emerging - but still expensive - technology of laser radar may be the best solution for detecting air turbulence that can hit commercial aircraft.

By John Rhea

BROOMFIELD, Colo. - A combination of conventional radar and the emerging - but still expensive - technology of laser radar may be the best solution for detecting air turbulence that can hit commercial aircraft.

This finding is according to experts at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., and at the NASA Dryden Flight Research Center at Edwards Air Force Base, Calif.

In a series of five flights completed last month from Jefferson County Airport in Broomfield, Colo., scientists from the two organizations used a light detection and ranging (LIDAR) instrument developed for NASA by engineers at Coherent Technologies Inc. of Lafayette, Colo. This LIDAR system detected clear-air turbulence at altitudes to 25,000 feet.

The test bed was the National Science Foundation (NSF) 35-year-old Lockheed Electra turboprop, similar to the aircraft that U.S. Navy pilots have used for many years for maritime patrol and anti-submarine warfare. The NSF aircraft accumulated about 15 flight hours for the tests.

In parallel, NCAR officials are testing a conventional radar in Juneau, Alaska, to detect convective turbulence from wind shear. Commercial aircraft now use airborne weather radars, but the purpose of the new research is to determine how engineers could team the two technologies into an integrated system to improve commercial aircraft safety.

Today there are no effective warning systems for clear-air turbulence, which occurs at high altitudes near jet streams and mountain ranges and as far as 50 miles from developing storm systems, NASA officials say.

Conventional radar monitors air turbulence by tracking raindrops or snowflakes. Powerful and highly sensitive radar such as the NEXRAD weather radar, however, can can monitor air turbulence by tracking insects, dust, and other air particles.

Earlier research on turbulence at the U.S. Air Force Wright Laboratory in Dayton, Ohio, used C-141 and C-130 transport aircraft and downward-looking LIDARs to measure the turbulence around drop zones for paratroopers.

The forward-looking LIDAR in the recent NCAR-NASA tests was sufficiently effective that "if an alarm were sounded when turbulence was first detected, passengers could have quickly returned to their seats and fastened their se at belts before the encounter," explains Rod Bogue, the project manager at the Dryden center.

The LIDAR operates in the infrared portion of the spectrum and measures the Doppler shift of the air particles relative to the aircraft.

Coherent Technologies engineers developed the LIDAR under a $2.2 million contract from NASA. Paul Reveley, the company`s director of business development, says he is talking with airline leaders about how to implement this technology.

At issue is how much warning time airline officials are willing to pay for, and what kind of production volume is necessary to drive down costs. Until these issues can be resolved, Reveley says he will not disclose the probable cost per aircraft

He does, however, say the system could be operational within three years.

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