A sonic anemometer uses ultrasonic transduction to measure wind speed, direction, temperature, and atmospheric changes. It can function in severe weather locations and has various models for specialized placement conditions. It has applications in weather monitoring, pollution control, building safety, wind farm planning, aviation meteorology, energy, disaster control, and civil engineering.
A sonic anemometer is an instrument that measures wind speed using solid-state ultrasonic transduction. It is designed to emit ultrasonic pulses between opposing transducers in order to measure the effect of a wind medium on the mechanical energy of acoustic vibrations. By electronically monitoring the transit times of pulses through a pair or multi-pair path, a sonic anemometer detects wind strength and direction and can infer other readings such as temperature and atmospheric changes.
Pulse transit measurements can be taken in one-, two-, or three-dimensional streams. Resolution is determined by the path length between the transducers, which is typically between about 4 inches (about 10 cm) and 8 inches (about 20 cm). Sonic anemometer devices provide even turbulent measurements with fine temporal resolution of 20 hertz (Hz) or more.
Because the speed of sound can be affected by temperature, these instruments can function as thermometers, although rain is known to vary the speed of sound. The lack of moving parts makes them suitable for use in severe weather locations, such as weather stations, buoys, and in other marine and aerospace placements. In design, they can be attached to brackets, poles or other support structures.
Measurements of various elements taken together enable the sonic anemometer to function; these include the distance between transducer faces located at opposite cardinal points; the speed of sound; gas flow speed; and the varying time it takes for an ultrasonic pulse to reach its opposing transducer. The tool compares the speeds of the pulses, such as traveling north to south and south to north respectively. Pulses traveling against the wind arrive later than those traveling against the wind; the two measurements are compared and the wind speed is calculated. Some tools also allow diagnostics to check the operation of the machine in atmospheric conditions with zero wind speed. Sometimes they are equipped with hygrometers, barometers and data loggers for analyzing humidity and barometric pressure.
Another key aspect of sonic anemometer technology is the robustness of its physical characteristics. There are various models for specialized placement conditions. For example, instruments made for saltwater are designed to be resistant to corrosion, a major advantage over traditional cup and vane anemometers. Technology that can measure from slight variations in wind conditions to changes due to large-scale solar heating is used in almost any environment.
Others are made to survive extreme temperatures and high wind speeds. Self-heating capabilities protect them from freezing. Sonic anemometers are also developed to withstand placement in hazardous populated environments such as industrial sites, offshore platforms, arctic stations and ocean-going vessels.
In field applications, sonic anemometer technology has other goals than weather station monitoring. These tools work in pollution control, building safety, agriculture, and a number of other contexts. They provide a small-scale analog for wind turbines by assessing year-round wind availability for wind farm planning. They also assist in aviation meteorology, energy, and disaster control. These devices also serve a variety of applications in urban, environmental and civil engineering settings and wherever wind condition analysis provides a vital element in decision making.
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