| For a science that is constantly in the lives of | | | | speed of sound depends on the speed and the |
| everyday folk, wind speed measurement certainly | | | | direction of the air that it passes through. A |
| manages to keep out of the public eye. The | | | | headwind slows sound down, and a tail wind |
| measuring of wind speed happens to be an | | | | speeds it up. An ultrasonic wind anemometer fires |
| important part of a number of everyday | | | | high-frequency sound pulses back and forth |
| technologies. Of course there is meteorology, the | | | | between two receivers. If the pulse takes more |
| measuring of weather phenomena, that wholly | | | | time travelling in one direction than the other, that |
| depends on the gauging of wind speed; but a | | | | is a sign that the slower trip had a headwind |
| surprising number of other everyday specialties | | | | working against it. The time differential helps |
| depend on wind speed measurements too, chief | | | | calculate the wind speed. You'll find these in use on |
| among them being aviation and marine and | | | | tall buildings, on weather buoys and at weather |
| navigation, stability management in skyscrapers, | | | | stations. |
| environmental sciences and disaster management. | | | | Another wind anemometer design that is |
| Wind measurement is done with a device known | | | | particularly ingenious is the constant-temperature |
| as a wind anemometer; though it might be argued | | | | anemometer. A thin wire held between two |
| that that is a redundancy since anemometer | | | | electrodes is heated up electrically to hold a |
| comes from the Greek Anemos = wind. | | | | constant temperature. A sensor measures the |
| Any device that measures wind speed is bound | | | | amount of current needed to hold the |
| to sense the pressure of it too. For this reason, | | | | temperature at ambient temperature levels. Any |
| many anemometer designs are successful when | | | | loss of temperature that is faster than would be |
| used as pressure meters too in addition. A version | | | | explained by the ambient temperature levels |
| of anemometer is known to have existed since | | | | would have to come from wind speed. This is a |
| around 1450. The modern wind anemometer | | | | particularly accurate method of measurement of |
| though, has been around for more than a century | | | | wind turbulence. However, like the laser |
| and a half now; the first successful design was | | | | measurement method below, this can be a quite |
| one that used a structure with four arms fanned | | | | inexpensive device to buy and maintain. |
| out, each one with a cup attached that caught | | | | Ultrasonic and constant temperature |
| the wind and spun the structure. The inventor, Dr. | | | | anemometers may be accurate enough for most |
| John Robinson, held the impression when he made | | | | purposes; but laser Doppler anemometers offer |
| his invention that any cup anemometer would | | | | extremely tight accuracy. A laser anemometer |
| share the characteristic that it would spin at a | | | | uses two laser beams; one that travels through a |
| third of the speed of the wind blowing past it, no | | | | sealed and clean pathway, and one that travels |
| matter what size it was built to be. Researchers | | | | through exposed air. The beam that travels |
| took his word at its face for quite a while before | | | | through the exposed air encounters dust particles |
| it was discovered that the size of design used | | | | that are borne along at the speed of the wind at |
| always affected the results. Researchers who had | | | | the point. The laser bounces off those dust |
| used the inventor's figures for their calculations | | | | particles, and measures by Doppler shift the |
| for years had to start over from scratch. | | | | speed at which the particle has been traveling. |
| Cup anemometers, these simple devices, are | | | | The Doppler shift is compared to what is |
| remarkably accurate machines today | | | | measured for the beam traveling through the |
| nevertheless; the best examples can approach a | | | | sealed tube and a relative measurement is made. |
| 99% accuracy level, and still be no more | | | | It would appear from these descriptions that |
| expensive than about $1000. But the cup | | | | anemometers always need to be large and |
| anemometer is still a mechanical technology that is | | | | permanent installations; as it happens though, small |
| prone to maintenance lubrication issues, friction, | | | | and inexpensive handheld versions with digital |
| mechanical damage and ice formation. There are | | | | displays exist for use by field researchers and |
| competing technologies that attempt to eliminate | | | | trainer pilots. The most striking feature of these is |
| the problems seen in the mechanical design. One | | | | the way they recognizably use nothing other than |
| of the most popular wind anemometer | | | | the same mechanics and structures of the |
| technologies in use today is the ultrasonic kind. | | | | professional devices, only miniaturized for handheld |
| The principle of the ultrasonic design is this: the | | | | use. |