An Inexpensive Sonic Anemometer for Eddy Correlation

A new continuous wave sonic anemometer was constructed using inexpensive ultrasonic transducers and phase-locked loop integrated circuitry. Vertical wind is measured by sensing the difference in phase between sound waves traveling in the +g and −z directions. The direction of sound travel is reversed 78 times per second, so the wind signal is updated at this frequency. Resolution is better than 1 cm s−1 and drift less than 3 mm s−1 K−1. Comparisons with a commercial sonic anemometer show excellent agreement between measurements from the two units.