What Measures Wind Speed?

Cup Anemometers

• Though basic in construction, the cup anemometer introduced in 1846 is considered an industry standard in measuring wind speed. Modern variants of this technology use three cups that spin around a vertical axis. The torque generated by the movement of wind is proportional to the wind speed. Cup anemometers must be calibrated because the torque also depends on the geometry of the cups used and the length of the arms they are attached to. Cup anemometers are relatively inexpensive and simple to construct, making them a popular project for science fairs.

Hot Wire Anemometers

• Hot wire anemometers exploit the electrical properties of metals to indirectly measure wind speed. The electrical conductivity of a metal wire is proportional to the temperature of the metal. A hot wire anemometer is essentially a fine metal wire that is heated above ambient temperatures. When wind blows, the wire is cooled, measurably reducing its conductivity. The degree to which the conductivity is reduced is proportional to the velocity of the wind. Hot wire anemometers are small and require electrical measurement equipment to use effectively.

Laser Doppler Anemometers

• Laser Doppler anemometers measure wind speed by examining how light is altered in interacting with particles carried on the wind. When laser light encounters small dust particles on the wind, they cause a Doppler frequency shift. The magnitude of this shift depends entirely on the speed of the particles. This indirectly measures the speed of the air around the device. Laser Doppler anemometers were introduced in 1976 to increase the accuracy of wind speed measurements.

Sonic Anemometers

• Sonic anemometers determine wind speed using ultrasonic time of flight measurements. These devices have multiple transducers that produce ultrasonic sound waves that travel through a small chamber open to the wind. The time required for the sound waves to travel across the chamber is proportional to the temperature and density of the air, which relies on wind speed. Sonic anemometers can measure wind speed along multiple dimensions simultaneously, providing more information about wind movement that allow for measurement of multidimensional turbulence.