What is an anemometer and wind sensor?

An anemometer measures wind speed. A wind sensor usually means a sensor that reports speed and direction, either as one combined unit (propeller vane, ultrasonic) or as an anemometer plus a separate wind vane. At aerodromes the terms are used loosely, so check whether a datasheet quotes direction as well as speed.

Wind pushes the cups round, and the rotor's turn rate is converted to speed, usually by counting pulses from a magnetic or optical pickup. The vane turns to point into the wind and an encoder or potentiometer reports its angle as direction. Both have bearings, so friction raises the wind speed at which they start to turn as they wear, and cup rotors tend to speed up faster in a gust than they slow down in a lull.

Pairs of transducers send sound pulses to each other in both directions. Wind speeds the pulse up in one direction and slows it in the other, so the difference in travel time gives the wind component along that path. Two or more paths give speed and direction. There are no moving parts to wear or freeze, and heaters keep the transducers clear in cold weather, but ice, deposits or heavy rain on the transducer faces can still affect the reading.

The standard measuring height is 10 m above ground, so readings from different sites can be compared. The sensor is placed where the wind is representative of the runway and clear of obstacles; WMO guidance is roughly ten times an obstacle's height as the minimum clear distance. On long or precision runways there is often more than one sensor set, and the meteorological authority decides the number and the positions.

Controllers and pilots use it to select the runway in use and to check crosswind and tailwind components. It feeds the local report on the tower display, ATIS and the METAR. Some aerodromes combine several anemometers into a low-level wind shear alerting system. The averaging period and direction reference differ between local reports and METAR, so the two figures are not always identical.

It is a separate meteorological system and not part of the series circuit, but it shares the site. The mast needs earthing and lightning protection, the signal and supply cables need surge protection, and the cable routes must be recorded and protected like any other airfield cable. At some aerodromes the wind data is carried to the same control room or SCADA as the lighting status.

Common faults are worn or iced bearings, failed heaters, water in connectors, a loose or mis-set vane that shows a constant direction offset, and damaged cable. Work on a mast near a runway needs the permit-to-work and the aircraft-movement controls. Lower a tilt-down mast rather than climbing it, isolate the supply first, and stay off the mast when lightning is near. Tell the meteorological authority before work starts, because the wind data is in use.