Posters

Abstract

This study explores the influence of enhanced sampling rates and reduced probe lengths on turbulent fluctuation measurements using the WindCube v2.1 lidar profiler, comparing it with another commercially configured WindCube v2.1. In the first experiment, a customized lidar sampled line-of-sight (LOS) velocities four times faster than the standard setup, resulting in a LOS velocity and wind speed sampling rate of 1 Hz and 4 Hz, respectively. This improvement was achieved by reducing the data collection accumulation time from each beam by 70%, accompanied by a corresponding 70% reduction in the number of transmitted pulses. The dataset used to assess the impact of the increased sampling rate on the measurement of turbulent fluctuations spans a 47-day period, divided into 2256 30-minute subsets. In another experiment, a customized lidar utilized a reduced probe length. In its standard commercial configuration, the WindCube v2.1 measures LOS velocity within a probe of approximately 23 m. The tailored version of the WindCube v2.1 lidar features a 50% reduction in pulse duration, resulting in a probe length reduction from 23 m to 15 m. The dataset used to evaluate the impact of the reduced probe length on the measurement of turbulent fluctuations covers a 33-hour period, divided into 66 30-minute subsets. The emphasis is on the along and cross-wind components, as well as the vertical velocity directly measured by beam 5. The data availabilities of the enhanced configurations are assessed, and their ability to measure turbulent fluctuations is evaluated through the calculation of standard deviation, with mean and interquartiles subsequently calculated. Furthermore, an analysis is conducted to assess the impact of both enhanced configurations on the spectral representation of LOS velocities. Specifically, volume-averaging within the probe is known to generate a deviation from the theoretically expected -5/3 slope within the inertial subrange of turbulence. This deviation is quantified for the probe length of the commercial configuration and the reduced probe length of the enhanced version. Additionally, the impact of the increased sampling rate on noise is examined through spectral analysis. Within spectra, noise is identified by the presence of a flattened portion at higher frequencies. The onset of this flattened portion depends on the spectral densities of the noise, which is directly proportional to the variance of noise. This variance is assessed for both commercial and enhanced configurations to determine the benefits of the latter in terms of extending the spectral domain available, thus enhancing its ability to capture the physics of smaller length scales of turbulence.