Direct Calculation of 3D Wind Speed from Propagation Times on Multiple Ultrasonic Paths

Abstract

An ultrasonic anemometer is one of the typical equipment that can be used to measure 3D wind speed. Most of commercially available ones consist of three 1D anemometers, and 3D wind speed is geometrically calculated from independently measured wind speed components. In addition, a time-division multiplexing, which is introduced to avoid the interference of bidirectionally transmitted sound waves, makes it difficult to shorten the response time of measurements. In this work, a new calculation method to directly obtain 3D wind speed from propagation times on multiple ultrasonic paths is proposed. The required number of the ultrasonic paths becomes four without using the time-division multiplexing. The requirement of bidirectional propagation is no longer necessary in the new method. Therefore avoiding interference, which is usually a problem with the measurements using continuous waves to improve the response time, becomes easier. The calculation of wind speed is reduced to solving a linear equation derived from Schotland's propagation model, and no prior information on sound speed is required. Proper arrangement of transducers is also discussed based on the linear equation. A wind tunnel test is conducted to verify the feasibility of the new method.