Vertical wind velocity measurements by a Doppler lidar and comparisons with a Doppler sodar.

A Doppler lidar based on a single frequency Ar(+) laser and a spherical Fabry-Perot interferometer is used to study the vertical velocity field in the planetary boundary layer. The wind velocity information is obtained by spectral analysis of the aerosol backscatter. The internal consistency of the lidar measurements points to a precision of 0.1 msec(-1) obtained for scans of ~25-sec duration and a good level of the received signal at a height of a few hundred meters and a vertical resolution of 75 m. A Doppler sodar was simultaneously operated to provide independent measurements of vertical velocity. The tests were carried out during nights characterized by horizontal winds <1 msec(-1). The axes of the two systems were displaced by 53 m, and the two beams overlapped only above ~300 m. The values of the correlation coefficient function between the two outputs for 100 data sets were ~0.5. A comparison of the velocity power spectra provided by the two systems shows good agreement at small values of the frequency; at large values, because of the limited spatial resolution of the sodar, its readings were consistently lower than those of the lidar.