Anemometer

An Anemometer is a meteorological instrument used to measure wind speed and, in many configurations, wind direction. At airfields, anemometers are essential for providing real-time wind data to pilots, air traffic controllers, and weather forecasters. The data is used to determine runway selection, approach and departure procedures, and to issue weather warnings. Modern anemometers use electronic sensors (cups, propellers, or ultrasonic transducers) that convert wind motion into electrical signals that are processed and displayed in knots, metres per second, or kilometres per hour.

Wind data exists because the direction and strength of the wind is one of the most operationally consequential variables at any airport — it determines which runway is safest to use, whether a crosswind exceeds an aircraft's certified limits, and whether departures or arrivals should be delayed until conditions ease. Without accurate, continuously updated wind measurement, both controllers assigning runways and pilots planning an approach or takeoff would be working from stale or estimated information in a situation where wind can shift meaningfully within minutes.

Because a tailwind or excessive crosswind component can compromise an aircraft's ability to land or take off within available runway length, or make directional control difficult during the roll, the anemometer's data directly underpins some of the most fundamental safety decisions made at an airport, from runway selection down to individual go-around calls.

Installed at airfields as part of the meteorological observation system. Typically located near the runway midpoint or at the touchdown zone, mounted on a mast or tower at a height of 10 metres above ground level (as recommended by ICAO and WMO). Used for aerodrome weather reporting, ATC wind information, and as input to automated systems such as RVR and weather displays. Also used at heliports, offshore platforms, and remote airstrips where wind data is critical for safe operations.

Mounted on a dedicated meteorological mast, or a cross-arm on a shared wind mast, sited so the sensor sits in open, unobstructed air. WMO and ICAO siting guidance calls for clearance from buildings, trees, and other masts of roughly ten times the height of the obstruction, to avoid turbulence and shadowing effects on the readings. Standard exposure height is 10 m above ground level (or above surrounding terrain on undulating ground), though a lower height is sometimes used near the runway touchdown zone where local practice or approach surface constraints apply. The mast is set on a concrete foundation with a lightning air terminal and dedicated earthing, since a structure of this height is itself a lightning risk in open terrain. Signal and power cabling run underground in duct back to the meteorological equipment shelter, and the sensor head is aligned to true (or magnetic) north during commissioning, since direction accuracy depends entirely on this reference being set correctly.

A cup anemometer uses three or four hemispherical cups mounted on a vertical shaft; wind causes the cups to rotate, and the rotational speed is proportional to wind speed. A vane (wind vane) is typically co-located to measure wind direction. Propeller anemometers use a horizontal-axis propeller that aligns with the wind. Ultrasonic anemometers use sound waves to measure wind speed and direction with no moving parts, offering higher reliability and lower maintenance. The instrument outputs electrical signals (analogue voltage, current, or digital data) that are processed by a display unit or fed into the airfield weather system.

Unlike the airfield ground lighting fixtures elsewhere in this library, the anemometer has no relationship to the constant current series circuit — it is a data source, not a load, and sits instead within the airfield's automated weather observation system. The sensor head's raw output (analogue voltage/current for cup and propeller types, or a digital serial stream for ultrasonic types) is passed to a signal conditioning unit or transducer at the mast base, then on to a data logger or data collection platform (DCP) that samples, timestamps, and averages the readings (typically as a 2-minute or 10-minute running mean, per ICAO/WMO reporting convention). The DCP reports over a wired or fibre link to the central AWOS/ASOS processor, which merges it with other sensor inputs to generate the wind entries in METAR/TAF products, the live wind readout on the controller's display, and ATIS broadcasts. Because each anemometer is individually addressed on this data network rather than sharing a current loop, a fault — a stuck cup, an iced vane, a stale or out-of-range reading, or a heater failure on de-iced models — is reported against that specific sensor ID, not as an ambiguous loop-wide fault requiring further sectionalised testing. Where multiple anemometers are deployed along a single runway (e.g., touchdown, midpoint, and stop-end for a long or CAT II/III runway), the AWOS processor reports each position's wind separately so controllers can identify localised wind shear or gust differences between the ends.

Anemometers are built around a weatherproof sensor head mounted on a mast or boom, with cup, propeller, or ultrasonic transducer elements fabricated from corrosion-resistant materials such as anodised aluminium, stainless steel, or UV-stabilised composite to withstand continuous outdoor exposure and, in cup or propeller types, high-speed rotation over years of service. The sensor head bearings are sealed, low-friction units, often with heating elements built into the housing or shaft to prevent icing that would otherwise stall the moving parts or bias readings in freezing conditions. The electronics enclosure, whether integral to the sensor head or mounted separately at the mast base, is potted or gasket-sealed to an IP65/IP67 rating and connects via shielded, weather-rated cable to the signal conditioning and output interface. The mounting mast itself is typically a rigid, corrosion-resistant pole set at the standard 10 m reference height, with the sensor head aligned clear of nearby obstructions and turbulence sources so wind measurements remain representative of the open-air flow. Cable glands, connectors, and junction boxes are all rated for continuous outdoor service and lightning-prone siting.