Doppler radar uses the principle of the doppler effect which says that the frequency of a sound or light wave changes if the object and/or the source of the wave generation is moving. If the object is moving toward the wave source the frequency increases, and if the object is moving away from the wave source the frequency decreases. Doppler radar sends out a microwave of known frequency and velocity. The return signal is analyzed to measure its frequency and the change in frequency is used to calculate the speed of the moving object.
Double doppler radar uses two signals and allows meteorologists to look inside a storm cloud to see if there is circular motion occuring which can indicate the possibility of tornadic activity. In this case, one frequency would show an increase, while the other would show a decrease meaning rotation within the clouds.
Doppler radar is an advanced radar system used by meteorologists to forecast weather patterns. It is a useful tool in determining when and where severe weather will form. Unlike conventional radar, Doppler is able to pick up characteristic circulation patterns in the atmosphere. This helps to identify severe weather like tornadoes. Doppler radar detects motion like air movement in clouds, this is called the doppler effect. When storms are approaching the vicinity of the radar, signals or pulses intensify. Meteorologists use these pulses to calculate the speed of approaching weather conditions. Doppler radar enables the meteorologist to predict weather formations quicker and more accurately than with the traditional system.
Atmosphere/Lutgens/ p. 347
A Doppler radar is a device that has a radio transceiver and receiver. The transceiver beams radiation at a particular frequency. When that radiation strikes a distant object, it reflects like light from a shinny object. The receiver then detects a small portion of the returning radiation. When the object is moving, the motion alters the frequency of the reflected wave. This change is detected at the receiver. The Doppler effect is commonly heard when a vehicle with a siren approaches, passes and recedes from an observer. The received frequency (pitch) is increased during the approach, it is identical at the instant of passing by, and it is decreased during the recession.
Weathermen often report on the Doppler radar image that is available from satellites. In this case, the same technology is being applied by radars to examine the motion if individual drops of precipitation.
A Doppler radar is a specialized radar that makes use of the doppler effect to produce velocity data about objects at a distance. It does this by beaming a microwave signal towards a desired target and listening for its reflection, then analyzing how the frequency of the returned signal has been altered by the object's motion. This variation gives direct and highly accurate measurements of the radial component a target's velocity relative to the radar. Doppler radars are used inaviation, sounding satellites, police speed guns, and radiology.