Sonic anemometer

A sonic anemometer measures wind from acoustic travel times between transducers. For path length $L$ aligned with velocity component $u$, the idealized transit times are $t_{+}=L/(c+u)$ and $t_{-}=L/(c-u)$, givingThe reciprocal-time difference removes the common sound speed in this model. Several paths recover a velocity vector. Transducer wakes, path averaging and precipitation can affect the measurement, so geometry and calibration matter when using it for turbulent fluxes.