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How does Doppler radar measure wind speed and direction?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Doppler radar
Weather forecasting Doppler radars, such as this one operated by the U.S. National Weather Service at New Underwood, South Dakota, extract the Doppler frequency shift of the echo produced by a moving target by noting how much the frequency of the received signal differs from the frequency of the signal that was transmitted.

Doppler radar measures wind speed and direction by detecting the Doppler frequency shift in radio waves reflected by precipitation particles, such as raindrops, that are carried along by the wind.12

The radar system calculates the radial velocity of these particles—the component of the wind moving directly toward or away from the radar installation. By measuring this shift as a function of the viewing angle, meteorologists can identify wind patterns. For example, rotation within a storm is indicated when the radar detects wind moving toward the antenna at one angle and away from it at a nearby angle.12

In addition to radial velocity, systems like Nexrad can determine wind direction by analyzing these velocity measurements across different angles and elevations. These radars also measure the spread in radial speed, which provides an indication of wind turbulence. By processing this data, forecasters can detect hazardous phenomena such as wind shear, mesocyclones, and rotating storm updrafts.12