Evolution of Sonic Anemometry - Brochure

1. Introduction

Credit for the first sonic anemometer should be given to Carrier and Carlson (Croft Laboratories, Harvard University), who in 1944 described a “true air speed indicator” for use on a blimp. Wind velocity would be obtained from measurements of the phase difference between signals received by two microphones placed upwind and downwind from a continuous source of sound. The instrument was never completed. In the early 1950s the idea was extended to measure horizontal winds using a single sound source and four microphones, equidistant from it at four cardinal directions on the compass. Again, nothing came of those efforts. To scientists trying to explore the atmospheric boundary layer in the mid-1950s, the sonic approach had great appeal. The hot-wire and hot-thermistor bivane techniques, available to them at the time, had serious limitations. The sonic anemometer offered rapid response, an open sampling volume and a calibration that could be calculated directly. It seemed especially suited for measuring the vertical wind component, badly needed for calculating turbulent transports of momentum, heat and water vapor near the ground.