Capabilities and Limitations of Lidar Regarding Turbulence Measurements in the Boundary Layer

During the Land-Atmosphere Feedback Experiment (LAFE), scanning thermodynamic research lidars for humidity and temperature measurements were combined with several Doppler lidars for line-of-sight wind measurements in a very special way. LAFE was organized in August 2017 at the Southern Great Plains Central Facility of the US Atmospheric Radiation Measurement (ARM) Program. The combination of in total eight lidar systems performed different types of synchronized scan patterns in order to investigate turbulent transport processes from just above the canopy height to the top of the atmospheric boundary layer (ABL). The turbulent fluctuations of temperature, moisture and the wind were observed simultaneously with remote sensing under different weather conditions. As advantage to in-situ techniques, lidar as active remote sensing technique captures the parameters of interest in a certain region continuously. As disadvantage, however, the statistical uncertainties – especially in daytime – may become significant and have to be considered carefully when deriving statistics of the turbulent fluctuations (variances and higher order moments, covariances). This last point is especially true for the temperature measurements with lidar which are based on the rotational Raman technique and thus use very faint inelastic backscatter signals. In this presentation, the capabilities and limitations of lidar regarding turbulence measurements in the ABL are discussed. For this, data of the LAFE campaign will be compared with data of previous campaigns and with the literature.

The photograph shows (left) the water vapor differential absorption lidar (DIAL) and (right) the temperature rotational Raman lidar (RRL) of the University of Hohenheim, Germany, at the ARM SGP site during LAFE.