What Is Wind Direction Measured With?

Determining wind direction has evolved through the use of different technologies for different specific purposes. The conventional in-situ, or on-site, measuring device is the anemometer. It is not always possible or practical to measure wind direction in-situ, thus alternatives techniques were developed. Today, direction is obtained throughout different levels of the troposphere and readings are fed to supercomputers for use in weather forecasting models.

Wind Socks and Kites

The simplest and earliest in-situ methods are feeling the wind, watching the clouds and watching other objects such as trees move as the wind blows. Basic tools like the wind sock and kite arose from these early methods. A wind sock is defined by the Random House Dictionary as "a tapered, tubular cloth vane, open at both ends and having at the larger end a fixed ring pivoted to swing freely..." they are still used where precise measurement is not needed. Kites were used to obtain data above the surface as early as the eighth century B.C. by the Eastern Zhou Dynasty in China.

Wind Vanes and Anemometers

Wind vanes have a nose and a tail. The vane moves about a vertical axis, the nose pointing toward the direction the wind is coming from. Anemometers are used to measure wind speed, however some, such as the sonic anemometer, also show direction. These are sometimes placed on things such as airplanes and weather balloons.

Doppler Radar

Using Doppler radar or next generation radar (NEXRAD) is common for both for research purposes and in determining general wind direction within a storm cell. The Doppler Effect is a term used for a shift in frequency which a NEXRAD measures to get velocity and direction of wind. A radial velocity radar image portrays wind direction in relation to where the radar is. This is useful for determining rotation within a storm. Dual Doppler is the concept of using two Doppler radars to get precise wind direction throughout the radar plot.

Satellite

Using satellite---mainly the Geostationary Orbiting Environmental Satellites, or GOES---to get direction involves making inferences based on patterns within clouds. The most useful cloud types for this purpose are those of the convective variety. Convection clouds form as the surface heats, and the warmer air rises, thus cooling and condensing. According to "An Introduction to Satellite Image Interpretation" a specific indicator of low level wind direction occurs in cumulus clouds that form just off the eastern and southern coasts of continents. The convective process here often causes clouds to form in "streets." The wind blows parallel to these streets, allowing direction to be inferred when these clouds are detected.

Light Detection and Ranging (Lidar)

Lidar is similar to radar, but instead of sending out radio waves, it sends laser beams that reflect back to the instrument. In the past lidar has been limited to research purposes. Researchers at the University of Stuttgart are working to integrate this device into wind turbines to increase blade control.

Resources

• Read this Article in Spanish
• Weather Underground: More on Next Generation Radar