The rest of the time, 59 minutes and 53 seconds, is spent listening for returns. For every hour, the radar spends a little more than 7 seconds actually transmitting pulses. The extremely short time that the transmitter is actually on means that the radar spends the vast majority of its time listening for returns. In between each transmitted pulse, the radar listens for returns. Each transmitted pulse only lasts 1.57 millionths of a second (0.00000157) and is repeated around 1300 times per second. The majority of the time, the radar will operate in short pulse mode. The radar has two operating modes: short pulse and long pulse. Radar pulses are transmitted away from the radar at the speed of light, but they are very short in duration. As the vehicle passes your location, the siren or whistle's pitch lowers. You may have heard this effect from an emergency vehicle or train. As an object moves away from your location, sound waves are stretched, resulting in a lower frequency. The phase shift is similar to the 'Doppler shift' observed with sound waves – sound from an object moving toward your location is higher pitch due to compression (a change in the phase) of sound waves. This phase shift is used to determine the velocity of the target. When the pulse hits a moving target, the phase of the returned wave is “shifted” or changed.

When the radar transmits a pulse, it keeps track of the phase and amplitude (shape, position, and form) of that pulse. In addition to range information, the WSR-88D is a Doppler radar, meaning that it can determine velocity of a target. By calculating the amount of time it takes for a pulse to be transmitted, strike a target, and return to the radar antenna, the system can determine the range (or distance) of the target from the radar. This means that the transmitter sends out very brief pulses of radio waves rather than a continuous stream of waves.

National Centers for Environmental Prediction.

Preparedness and Mitigation: Individuals (You!).

Preparedness and Mitigation: Communities.The Positive and Negative Side of Lightning.

West united states doppler radar