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Early Tests Show Air Turbulence Sensor Could Make Air Travel Safer

Dwayne Brown
Headquarters, Washington, DC                        April 6, 1998
(Phone:  202/358-1726)

Kirsten Williams
Dryden Flight Research Center, Edwards, CA
(Phone:  805/258-2662)

Kathy Barnstorff
Langley Research Center, Hampton, VA
(Phone:  757/864-9886)

Anatta 
National Center for Atmospheric Research, Boulder, CO
(Phone:  303/497-8604)

RELEASE:  98-57

EARLY TESTS SHOW AIR TURBULENCE SENSOR COULD MAKE AIR TRAVEL SAFER

     NASA is testing a new sensor that could make air travel safer 
by detecting previously invisible forms of clear air turbulence 
and giving pilots time to take safety precautions.  Early tests of 
the new clear air turbulence sensor are promising, officials say.

     Clear air turbulence is an invisible safety hazard for 
aircraft.  Though seldom damaging to modern aircraft, which are 
designed to withstand its stresses, it is the leading cause of in-
flight injuries among the flying public.

     "During the tests, the system observed turbulent regions of 
air ahead of the aircraft as it moved forward.  The aircraft 
experienced disturbances as it penetrated the turbulence.  In that 
scenario, if an alarm were sounded when turbulence was first 
detected, passengers could have quickly returned to their seats 
and fastened their seatbelts before the encounter," said project 
manager Rod Bogue of NASA's Dryden Flight Research Center, 
Edwards, CA.

     Flights of the detector originated from Jefferson County 
Airport, near Broomfield, CO.  The experiment was flown on three 
separate flights for a total of more than seven hours at altitudes 
as high as 25,000 feet.  Additional flights are slated to add to 
the turbulence database and to fine-tune the sensor for better 
measurements.

     Currently there are no effective warning systems 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.  It's been referred to as 
"rough air" or "air pockets," that can be felt, but not seen.

     The sensor device, called Airborne Coherent LiDAR for 
Advanced In-flight Measurement, was designed and built by Coherent 
Technologies Inc., Lafayette, CO, for NASA.  It relies on 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 on infrared light waves.

     "The infrared radar concept uses a light pulse 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.

     During its 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 they experienced.  In this way, the team is exploring 
the relationship between the laser radar-measured turbulence 
characteristics and the actual turbulence experienced by the 
aircraft.  These tests are designed to provide 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, CO.  "Through this new 
device and turbulence research conducted at NCAR, we expect a 
clearer picture to emerge to make flying safer."

     Dryden is using an aircraft owned by the National Science 
Foundation and operated by NCAR.  NCAR is managed by the 
University Corporation for Atmospheric Research under sponsorship 
by the National Science Foundation.  Other partners for the 
project include NASA's Langley Research Center, Hampton, VA; 
NASA's Marshall Space Flight Center, Huntsville, AL; Coherent 
Technologies, Inc.; Global Hydrology and Climatology Center; 
Huntsville, AL; Boeing Commercial Airplane Group, Seattle, WA, and 
the Air Force Research Laboratory Sensor Directorate Multifunction 
Electro-Optics Branch, Dayton, OH.

     Langley is the Agency's lead center for the NASA Aviation 
Safety program.  Other participating NASA centers include Dryden, 
Ames Research Center, Moffett Field, CA, and Lewis Research 
Center, Cleveland, OH.

                             -end-