Weather station/Sonic anemometer

Sonic Anemometer
Sonic Anemometer, is a instrument which uses ultrasonic sound waves to measure wind velocity.

An ultrasonic anemometer has two or three pairs of sound transmitters and receivers mounted at right angles to one another. Stand it in the wind and each transmitter constantly beams high-frequency sound to its respective receiver. Electronic circuits inside measure the time it takes for the sound to make its journey from each transmitter to the corresponding receiver. Depending on how the wind blows, it will affect some of the sound beams more than the others, slowing it down or speeding it up very slightly. The circuits measure the difference in speeds of the beams and use that to figure out how fast the wind is blowing.