September 2003
(un)Fasten your Seatbelts
By Patrick Barry and Dr. Tony Phillips
The "fasten seatbelts" light turns off, and you get up to ask the stewardess for
a pillow; it's going to be a long flight. Only a kilometer ahead in the
cloudless sky, a downward draft of sheering winds looms. When the plane hits
these winds, the "turbulence" will shake the cabin violently and you could be
seriously hurt.
You don't know about those winds, of course, and neither does the pilot. Today's
weather satellites can't see winds in clear skies: they rely on the motion of
clouds to infer which way the winds are blowing.
"Believe it or not, their best indication of wind sheer right now is warnings
from aircraft that have gone through it ahead of them," says Bill Smith of
NASA's Langley Research Center.
But a new satellite technology being pioneered by NASA and NOAA could improve
this shaky situation. It's called GIFTS, short for Geosynchronous Imaging
Fourier Transform Spectrometer. GIFTS is an infra-red sensor that can detect
winds in cloudless skies by watching the motions of atmospheric water vapor.
Water vapor is mostly invisible to the human eye, but it reveals itself to GIFTS
by the infra-red radiation it absorbs.
 |
| EO-3, carrying the GIFTS
instrument, will be in a geosynchronous orbit for extended monitoring of large regions of our planet and enabling observation of weather patterns at higher resolution than possible with existing geostationary satellites. |
Smith is the lead scientist for EO-3, a
satellite designed to test out this new technology. Slated for launch in 2005 or
2006, EO-3 will carry GIFTS to Earth orbit where it can produce 3-dimensional
movies of winds in the atmosphere below.
These wind data will not only improve safety, but also help the airlines save
money. Knowing the winds along a flight route allows airlines to adjust the
plane's fuel load accordingly, thus reducing the weight that the engines must
lift. Saved fuel means saved money and less pollution.
GIFTS can help planes avoid another potentially lethal problem, too: Ice forming
on their wings. If a cloud contains "supercooled" water droplets whose
temperature is below freezing, those droplets will form ice on the wings of
planes that pass through it. By looking at about 1700 different frequencies of
the light coming from clouds, GIFTS can measure the temperature of the cloud top
and determine whether it contains water droplets that could cause aircraft
icing. With information from GIFTS in hand, pilots can simply avoid clouds that
appear dangerous.
Once EO-3 demonstrates the accuracy of GIFTS, airlines will be able to
capitalize on this potential to make flying a cheaper and safer experience.
Learn more about the GIFTS instrument and other advanced technologies being
tested on the EO-3 mission at
http://nmp.jpl.nasa.gov/eo3. Kids can go to The Space Place to play a data
compression game related to EO-3 at
http://spaceplace.nasa.gov/eo3_compression.htm.
This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.