Reported December 2007

BACKGROUND: Weather forecasters in the middle of the U.S. are making better local predictions for pilots and others thanks to an airborne sensor being tested by NASA’s Aviation Safety Program. Dozens of commuter aircraft have been equipped with the Tropospheric Airborne Meteorological Data Report (TAMDAR) instrument. The information collected benefits weather models and forecasts because it increases the number of observations in the lower atmosphere. Larger airplanes fly above most weather and collect less data from the atmosphere.

HOW IT WORKS: TAMDAR is a tiny sensor that allows aircraft to automatically sense and report conditions in the atmosphere. Observations are sent by satellite to a data center on the ground that processes and distributes up-to-date weather information to forecasters and pilots. Initial research shows that the airborne sensor makes a forecast model that's 10 to 20 percent more accurate, with just the temperature being taken into account. It also measures humidity, pressure, winds, icing, and turbulence with the help of the Global Positioning System (GPS), which adds information on location, time and altitude into the mix. Meteorologists at the National Weather Service have found tat TAMDAR is useful in forecasting severe thunderstorms, dense fog, winter storms, and low-level wind shear.

ABOUT GPS: The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use a combination of signals to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.

HOW MANY POINTS? A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2-D position (latitude and longitude) and to track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time.

The Institute of Electrical and Electronics Engineers, Inc., and the American Meteorological Society contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Dr. Taumi Daniels, Electrical Engineer
NASA Langley
(757) 864-4659
taumi.daniels@nasas.gov

American Meteorological Society
(617) 227-2425
http://www.ametsoc.org

For more information about the latest technologies that measure the weather:

Institute of Electrical and Electronics Engineers,
Inc. IEEE-USA
(202) 785-0017
http://www.ieee.org
ieeeusa@ieee.org

DID YOU KNOW?

There are only 70 weather balloon sites in the continental United States that collect temperature, wind and moisture data from twice-daily atmospheric soundings. The TAMDAR experiment added 800 more daily atmospheric soundings.