While launching gliders at Front Royal, VA (KFRR) over the weekend, a fellow pilot and I got curious about the airport's weather equipment. We know that KFRR has local equipment to measure wind speed and direction. There is a screen in the FBO that shows a graphical readout of the wind situation. However, it was not obvious looking at the equipment itself how this is done.

Here are two pictures I took:

enter image description here

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Nothing on either of these two pieces of equipment was actively spinning or being visibly affected by the wind. At the time we has a 10-12 knot headwind almost directly down the runway. This equipment is ~40 feet to the left of the runway threshold.

Question: Is one of the pieces of equipment I've photographed responsible for measuring wind speed? If so, how?

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    $\begingroup$ Hey, would you mind adding your imagery to weather.gladstonefamily.net/site/KFRR, as it looks to be a public resource for ASOS station imagery? $\endgroup$ – JeopardyTempest Jun 27 '17 at 0:04
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    $\begingroup$ @JeopardyTempest Done. I've also adjusted the marker on the satellite map to one of the two "parts" of the installation. $\endgroup$ – bclarkreston Jun 27 '17 at 19:33

The device used to measure wind speed is called an anemometer. The one that spins with 3 spoon-like arms is just one type. There are some that have a propeller or fan that spins like a windmill. There are other types that aren't so obvious, such as the ultrasonic anemometer that has no moving parts, but instead uses ultrasonic sound waves to measure wind velocity, it was developed in the 1950s. (https://en.wikipedia.org/wiki/Anemometer)

Actually, if you zoom in on your second photograph you can see the ultrasonic anemometer immediately above the lights on the tower, and below the very top of the tower. It looks like three vertical fingers pointing up.

Zoom Ultrasonic Anemometer

Also, since you are a pilot, you are already familiar with another type of anemometer that doesn't have moving parts, a pitot tube is a type of anemometer. So long as the pitot tube weathervanes into the wind, it can be used to measure wind speed as well.


Ultrasonic anemometers are replacing the traditional cup anemometers in automated weather stations. The sensor measures the time it takes for an ultrasonic pulse to travel between the probes, which is affected by wind speed. In your second image, the object directly above the lights appears to be an anemometer.

Ultrasonic wind sensor


Ultrasonic sensors have the advantage of no moving parts and lower maintenance requirements. Also, with additional probes, they can measure the wind in 3D.

  • $\begingroup$ Thanks fooot and @Devil07 for your answers, both the same and both correct (I assume from the votes). Very helpful! I'm not sure what the protocol is when two answers are correct, since I can only check one of them. Veterans please advise! $\endgroup$ – bclarkreston Jun 26 '17 at 22:44
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    $\begingroup$ @bclarkreston -- pick whichever answer you found more helpful :) $\endgroup$ – UnrecognizedFallingObject Jun 26 '17 at 23:23
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    $\begingroup$ Here is direct information on ASOS stations showing that ball and cup anemometers have been the standard, but can be replaced by sonic anemometers in locations that have freezing issues. No idea if there is a newer push to further move towards sonic anemometers network-wide. $\endgroup$ – JeopardyTempest Jun 27 '17 at 0:03
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    $\begingroup$ Thanks @JeopardyTempest...yours is arguably the most detailed response, as the linked PDF very thoroughly explains each piece of equipment used in an ASOS station. $\endgroup$ – bclarkreston Jun 27 '17 at 14:26
  • $\begingroup$ Like the ultrasonic type, Hot-wire anemometers have no moving parts - they measure airflow / wind speed based on how much heat is dissipated from a wire, although these are rarely used for atmospheric measurements. $\endgroup$ – kabZX Jun 27 '17 at 22:38

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