Experiences with Doppler Lidar based routine turbulence measurements

At the Lindenberg Meteorological Observatory - Richard Aßmann Observatory (MOL-RAO), StreamLine Doppler Lidar (DL) systems from the manufacturer HALO Photonics (nowadays HALO Photonics by Lumibird) are tested for a routine application to derive profiles of turbulence variables within the atmospheric boundary layer (ABL). Information from these profile measurements is useful to get a better understanding of ABL processes and to provide enhanced insights into the ABL vertical structure under different weather conditions and over the course of a diurnal cycle (e.g. stable ABL, convective-mixed ABL, transitions between different ABL states). Further possible applications of turbulence profiles from DL measurements can be found in the area of ​​validation and/or development of turbulence closure schemes used in weather or climate models and in the wind energy sector.

As an example, results for the turbulence kinetic energy (TKE) derived by means of a DL scanning and turbulence retrieval method introduced by Smalikho and Banakh (2017) are presented. For the retrieval of TKE profiles this method provides two correction terms. One corrects for an underestimation of TKE due to the averaging of radial velocity over the pulse volume and the other is used to prevent an overestimation of TKE if turbulence is very weak. The long-term measurements at MOL-RAO are used to evaluate the performance of these correction terms. It is shown that the corrections can have a significant positive effect on the precision and accuracy of the retrieved TKE, provided that noise-free DL radial velocity measurements are used as input data for the turbulence retrieval and the inherent assumptions of the retrieval method are fulfilled. To verify the latter, an additional data quality control (QC) scheme was developed at MOL-RAO and applied after the retrieval procedure. Insights into the main test criteria of this QC scheme will be presented and the results of their application will be discussed.  

Finally, comparisons of DL based TKE retrievals are shown between seven different DL systems which were operated side-by-side with an identical scan configuration under same atmospheric conditions. The DL systems exhibited differences in their pulse lengths and thus the size of their pulse volumes. The associated differences in the correction terms and their effect on the final TKE retrieval results will be discussed.     

References

Smalikho, I. N. and Banakh, V. A.: Measurements of wind turbulence parameters by a conically scanning coherent Doppler lidar in the atmospheric boundary layer, Atmos. Meas. Tech., 10, 4191–4208, https://doi.org/10.5194/amt-10-4191-2017, 2017.