How Do Ultrasonic Wind Sensors Work?

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Ultrasonic Wind Sensor at Work

Youre standing on the sailboats bow on a windy day, facing the helm and yelling There is a rock ahead. Youre doing this while youre turning forward to look again. What the helmsman hears is There is a…..

Sound waves propagate through the air, and as you turned your mouth (the speaker) away from the direction of the helmsman, the wind blew those sound waves away. Ultrasonic wind sensors can measure this effect.

The distances between the sensors are close enough together that the sound waves arent blown away, and in windless conditions, the speed of sound is consistent and known. Each of the three sensors takes a turn at high frequency yelling while the other two listen.

The time it takes for each listener to hear the yelling is very accurately measured. Apply a lot of calculations, and you can derive both apparent wind direction and speed. As an example, if the wind is from aft of a transceiver, it will push the sound waves a little faster and they arrive earlier. Inversely, if the wind is blowing toward the transceiver, it slows down the sound waves, and it takes them longer to reach the other listeners. The difference in the time it takes to reach each listener is used to triangulate the direction the wind is traveling. This is a very simple explanation of a complex process.

Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills techniques required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.

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