Anemometer is a fancy name of a device which measures wind speed and direction. We are used to see mechanical spinning devices that rotate and thus indicate speed strength and direction. As we know, mechanical things aren’t always reliable especially in rough conditions. In other hand, ultrasonic anemometer can be more sensitive and precise. Lfaessler have written a series of build posts of ultrasonic wind meter.
His design uses four pairs of ultrasonic transducers that are positioned perpendicularly. By knowing ultrasound speed in the air, it is possible to determine wind speed and direction from ultrasound speed change. All four transducers are controlled by Arduino which takes care of correct signal routing and measuring time between sent and received signals. Arduino also calculates wind direction in 2D plane and its speed. Since received ultrasonic signal is weak, he designed amplifier to make them acceptable for Arduino input. There are intense testing and tuning involved in this part, since it is important to sense received signals correctly in order to get precise readings. After initial testing and build, project ended in to nice Arduino anemometer shield where analog and digital parts of circuit seems to be working fine. Recently Arduino library was released that takes care of all complex programming.