Turbulence Measurements with Dual-Doppler Scanning Lidars

Abstract

Velocity-component variances can be directly computed from lidar measurements using information of the second-order statistics within the lidar probe volume. Specifically, by using the Doppler radial velocity spectrum, one can estimate the unfiltered radial velocity variance. This information is not always available in current lidar campaigns. The velocity-component variances can also be indirectly computed from the reconstructed velocities but they are biased compared to those computed from, e.g., sonic anemometers. Here we show, for the first time, how to estimate such biases for a multi-lidar system and we demonstrate, also for the first time, their dependence on the turbulence characteristics and the lidar beam scanning geometry relative to the wind direction. For a dual-Doppler lidar system, we also show that the indirect method has an advantage compared to the direct one for commonly-used scanning configurations due to the singularity of the system. We demonstrate that our estimates of the radial velocity and velocity-component biases are accurate by analysis of measurements performed over a flat site using a dual-Doppler lidar system, where both lidars stared over a volume close to a sonic anemometer at a height of 100 m. We also show that mapping these biases over a spatial domain helps to plan meteorological campaigns, where multi-lidar systems can potentially be used. Particularly, such maps help the multi-point mapping of wind resources and conditions, which improve the tools needed for wind turbine siting.

Evidence of Ocean Waves Signature in the Space–Time Turbulent Spectra of the Lower Marine Atmosphere Measured by a Scanning LiDAR

“…Driven by the growth in remote-sensing applications for weather forecasting and wind energy exploitation, LiDAR technologies and post-processing techniques have experienced a rapid growth over the last 20 years. A wide range of applications are referred to in [50], including weather and climate monitoring and forecasting (c.f. [51,52]), fundamental studies in turbulent flows and the ABL (c.f.…”

“…Here, the wave influence in the MABL was investigated within the WBL through original field measurements taken by a scanning Light Detection and Ranging (sLiDAR) system employed on the coast. The sLiDAR-specific literature review ( [50][51][52][53][54][55][56][57][58]) is presented in Section 2.2.1. Operating in staring mode, i.e., staring in a single direction with fixed line of sight (LOS), the sLiDAR registers highly detailed space-time mappings of the radial wind speed (RWS), here approximating the longitudinal wind velocity.…”

Coastal Wind Measurements Using a Single Scanning LiDAR

“…The choice of scanning mode depends on the purpose of the measurements. The RHI mode and the fixed mode are frequently used for wind turbine wake measurements [15,16] and virtual met tower measurements [24], respectively. The current study uses the PPI mode, as it is compatible with the VVP method [25][26][27] for retrieving horizontal wind speeds and directions from the LiDAR-measured radial wind speeds.…”

“…Therefore, they offer the potential for assessing offshore wind from the coast, thus obviating the need for offshore met masts or floating LiDARs [10][11][12]. To date, scanning LiDARs have been used for the measurements of wind fields and, most importantly, turbulence in single or multi-LiDAR modes [13][14][15][16]. Scanning LiDARs have also been used in the measurements of flow fields around a wind turbine or to evaluate wind turbine power performance [17,18].…”

CW Direct Detection Lidar with a Large Dynamic Range of Wind Speed Sensing in a Remote and Spatially Confined Volume

“…Doppler wind lidar (DWL) has matured over the past few decades mainly due to developments in laser sources and detector systems. With the ability to perform remote and spatially resolved wind sensing, DWL has become an indispensable tool for many applications including the study of dynamic properties of the atmospheric boundary layer [1], the detection of aircraft wake vortices [2,3], air turbulence [4][5][6] and wind shear [7]. Recently, cost-efficient and eye-safe DWL systems have emerged as a promising alternative wind sensors for wind turbine control [8].…”