A Doppler Lidar technique for monitoring the „whole“ boundary layer

Doppler Lidar is a powerful measuring technique for observing particularly vertical wind profiles in the atmospheric boundary layer. It is well known that the performance of such long-range wind lidars depends to some extent on the atmospheric conditions, which causes a variable upper limit of the accessible measuring heights. Another, more fundamental constraint of long-range lidars refers to the lower height limit which is typically > 50 m. Furthermore, useful profiling in these height ranges requires range resolution much finer than the height range itself. An adequate range resolution causes broad Doppler spectra which result for typical Lidar wavelengths (1 – 1.5 um) in an unacceptable poor velocity resolution.

The height range below 50 m plays a key role for the interaction between surface and atmosphere and can show sharp and sometimes complex gradients as for example in nocturnal stable layers. The diurnal evolution of the profile of mean wind and turbulence close to the surface can be quite different from higher layers and cannot be inferred from upper height observations.

 A combination of Lidar techniques has been developed to overcome the above-mentioned lower range limitation and to extend the lower height range down to < 10 m while preserving the long-range capability.

Field data from such recently developed Lidar system will be presented in comparison with composite profiles from simultaneous measurements with a conventional long-range pulsed Doppler Lidar, a short-range FM-CW-Lidar and a 15 m mast with sonic instrumentation. The analysis will include profiles of mean wind as well as of turbulence parameters.