A comparison of acoustic Doppler vertical velocities with direct measurements in the atmospheric boundary layer

Abstract

THE quantitative evaluation of the intensity of acoustic echoes from the first few hundred metres of the atmospheric boundary layer (in both stable and convective situations) has been the subject of much recent experimental work^1–5. The acoustic echo, however, contains Doppler information on the vertical air motion and this could prove of great use in the specification of further important boundary layer statistics such as σ_w², the variance of the vertical wind speed⁶ and ɛ, the rate of dissipation of turbulent kinetic energy. Beran et al.⁷ using a sounder in the monostatic mode (transmitter and receiver aerials located together) derived the profile of the vertical wind component using the acoustic Doppler technique. They did not, however, verify that the estimates of the winds were correct, nor did they record the magnitudes of the Doppler shifts in the weak echo regions between the periods of thermal activity. This paper presents a quantitative comparison between acoustic Doppler vertical winds and direct estimates measured at a fixed height in the atmosphere.