RADAR

The term radar is a short way of saying RAdio Detection And Ranging, and was first used during WWII. A radar is a special kind of radio capable of sending out and receiving the same signal. As these radio waves leave the radar, they can encounter a wide range of phenomena in the atmosphere, ranging from dust, to rain and snow, to birds and airplanes. Due to the particular wavelength of the radar's signal, weather targets like raindrops and snowflakes can be best detected. The radio waves reflect off the targets and return to the radar to produce bright images on television-like radar screens. The images, called echoes, are used to determine the strength of a target and the distance and direction of a target from the radar.

The name Doppler comes from the term the Doppler Effect. A 19th century scientist by the name of J.C. Doppler recognized that sound waves seem to change frequency - and therefore pitch - as they are reflected from a moving object. He discovered this by spending his time listening to train whistles. You see, a whistle of an approaching train sounds higher than that from a train moving away. Radar signals behave the same way. The Doppler weather radar uses the Doppler Effect to determine speed and direction of wind-driven precipitation. The radar sends out pulses of radio waves, which are reflected back by the moving targets. A change in frequency of the return signal indicates a change in the wind direction and speed.

It wasn't until the mid 1980's that the concept of the Doppler Effect was introduced to weather radars. The Doppler weather radar in the Eureka office is a highly sensitive radar. It is able to detect anything from a sea gull to fine dust, but the prime use is to detect water droplets that can be found in rain producing clouds. The optimum range of the radar is 125 nm, but can detect targets up to a distance of 250 nm. The radar's sensitivity allows smaller targets to be detected and assigns a movement to the particle. This tool is useful in finding small scale air circulations.

Webmaster
US Dept of Commerce
National Oceanic and Atmospheric Administration
National Weather Service
Spokane Weather Forecast Office
2601 N. Rambo Rd.
Spokane, Washington 99224

Tel: (509) 244-0110