There has been no effective warning system for clear air turbulence, which occurs at high altitudes near jet streams and in the vicinity of mountain ranges and as far as 50 miles or more from developing storm systems.

The device, called Airborne Coherent LiDAR for Advanced In-flight Measurement, was designed and built by Coherent Technologies Inc., Lafayette, Colo., for Dryden. It relies upon a form of laser technology, called Light Detection and Ranging (LiDAR), to detect changing velocities of tiny particles in turbulent air. As long as the wind velocity remains uniform, no turbulence exists. But if the laser beam detects changes in the velocity, it's a clear indication of turbulence ahead. The laser technology is similar to the more familiar radar and can be envisioned as a kind of infrared radar. Although conventional radar uses radio waves, this laser technology relies upon infrared light waves.

"The flight covered altitudes up to and including 25,000 feet. During the more than two-hour system checkout flight, the sensor performed quite well, and nearly all objectives were achieved," Dryden Project Manager Rod Bogue said. "Several days will be needed to perform detailed analysis so that performance can be confirmed. " The infrared radar concept uses a light pulse that is transmitted from the laser, and some of the light is reflected off the particles back to a sensor at the source," Bogue said. " The reflected light has a slight shift in frequency, called a Doppler shift, due to the aircraft 's motion relative to the particles. By analyzing the frequency of the Doppler shift, the changes in wind velocity along the laser beam's path can be determined, " he said.

Depending on the power of the laser and the concentration of the airborne particles, the new infrared radar system is expected to be able to detect dangerous turbulence in enough time to avoid injury.

During this first flight, the flight crew located turbulent conditions and used the infrared radar to measure the changes in wind speed - a measure of turbulence - before flying through the disturbed air. Once the aircraft reached the turbulence, the crew compared the pre-encounter measurements with the effects of the turbulence it experienced. In this way, the team is exploring the relationship between the laser-measured turbulence characteristics and the actual turbulence experienced by the aircraft. These tests are slated to provided an efficient checkout of the flight hardware and to help characterize turbulence measurements.

"Not much is known about accurately detecting and forecasting turbulence," said Larry Cornman, scientist for the National Center for Atmospheric Research (NCAR), Boulder, Colo."Through this new device and turbulence research conducted at NCAR, we expect a clearer picture to emerge. Our goal is to provide accurate detection devices and reliable warnings that will make air travel safer and more comfortable in the future."

Dryden is using an L-188 Electra aircraft, owned by the National Science Foundation and operated by NCAR, because of its ready availability and capabilities. NCAR is managed by the University Corporation for Atmospheric Research under sponsorship by the National Science Foundation. Other partners are NASA's Langley Research Center, Hampton, Va.; NASA's Marshall Space Flight Center, Huntsville, Ala.; Coherent Technologies Inc.; Global Hydrology and Climatology Center; Huntsville, Ala.; and Boeing Commercial Airplane Group, Seattle, Wash.

The first flight of the detector, originated from Jefferson County Airport near Broomfield, Colo. Follow-on flight tests may include testbed aircraft representative of those in current commercial service. Possible aircraft could include the DC-8, a NASA Airborne Science Program aircraft, based at Dryden and a Boeing 757 aircraft based at Langley.

Turbulence research is part of NASA's Aviation Safety Program, created in response to a report from the White House Commission on Aviation Safety and Security, led by its chairman, Vice President Al Gore. NASA's goal is to reduce the fatal aircraft accident rate by 80 percent in 10 years and by 90 percent in 20 years. To reach that goal NASA has formed a partnership with the Federal Aviation Administration, the aviation industry and the Department of Defense.

Langley is the Agency's lead center for the program. Other participating NASA centers include Dryden; Ames Research Center, Moffett Field, Calif.; and Lewis Research Center, Cleveland, Ohio.

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Responsible NASA Official: John Childress For questions, contact: Dryden Web Group Page Curator: Marty Curry Modified: March 31, 1998