Methodology for obtaining wind gusts using Doppler lidar

Abstract

A new methodology is proposed for scaling Doppler lidar observations of wind gusts to make them comparable with those observed at a meteorological mast. Doppler lidars can then be used to measure wind gusts in regions and heights where traditional meteorological mast measurements are not available. This novel method also provides estimates for wind gusts at arbitrary gust durations, including those shorter than the temporal resolution of the Doppler lidar measurements. The input parameters for the scaling method are the measured wind‐gust speed as well as the mean and standard deviation of the horizontal wind speed. The method was tested using WindCube V2 Doppler lidar measurements taken next to a 100 m high meteorological mast. It is shown that the method can provide realistic Doppler lidar estimates of the gust factor, i.e. the ratio of the wind‐gust speed to the mean wind speed. The method reduced the bias in the Doppler lidar gust factors from 0.07 to 0.03 and can be improved further to reduce the bias by using a realistic estimate of turbulence. Wind gust measurements are often prone to outliers in the time series, because they represent the maximum of a (moving‐averaged) horizontal wind speed. To assure the data quality in this study, we applied a filtering technique based on spike detection to remove possible outliers in the Doppler lidar data. We found that the spike detection‐removal method clearly improved the wind‐gust measurements, both with and without the scaling method. Spike detection also outperformed the traditional Doppler lidar quality assurance method based on carrier‐to‐noise ratio, by removing additional unrealistic outliers present in the time series.

Characterizing wind gusts in complex terrain

“…Further, the volumetric averaging inherent in the use of lidars means the wind speeds are not directly equivalent to those from in situ anemometry. Nevertheless, vertically pointing Doppler lidars offer the po- tential to quantify wind gusts at heights above those possible from sonic anemometers deployed on meteorological masts (Suomi et al, 2017) and are increasingly being adopted by the wind energy research and operations communities (IEA Wind Task 32 lidar for wind energy deployment) (Clifton et al, 2018). Herein, we evaluate the degree to which the probability distribution of gust amplitudes and GFs derived from the maximum of the disjunct measurements sampled at each of 10 heights (effective duration of ≈ 2 s) in each 10 min period correspond to those from the 18 Hz data from the sonic anemometers.…”

Current gust forecasting techniques, developments and challenges

“…Cheng et al (2012b) address the development of improved physically-based gusts parametrisations, with an emphasis on the gust profile. Suomi et al (2013Suomi et al ( , 2015Suomi et al ( , 2016Suomi et al ( , 2017 characterise gust profiles using measurements and pursue the development of gust parametrisations in this context. Efthimiou et al (2017b, a) model the underlying wind distribution giving rise to gusts as extreme values, using direct numerical simulation (DNS) and wind tunnel measurements to inform and validate the model, which can be applied at any height, also testing at field sites.…”

A Review of Progress and Applications of Pulsed Doppler Wind LiDARs

“…Manufacturer Halo Photonics suggests a threshold SNR of −18.2 dB for their StreamLine LiDAR, while tests under quiescent atmospheric conditions suggest a value of −20 dB for the same instrument, resulting in a 40% increase in data availability [34]. In addition, to better estimate the ratio of the wind gust speed to the mean wind speed, Suomi et al [39] suggested using the spike removal technique instead of SNR threshold for data filtering.…”