27 Sep 2023
 | 27 Sep 2023
Status: this preprint is currently under review for the journal WES.

Experimental evaluation of the motion-induced effects on turbulent fluctuations measurement on floating lidar systems

Nicolas Thebault, Maxime Thiébaut, Marc Le Boulluec, Guillaume Damblans, Christophe Maisondieu, Cristina Benzo, and Florent Guinot

Abstract. This study investigates the impact of motion on the line-of-sight (LOS) turbulent velocity fluctuations derived from lidar profiler measurements. Onshore tests were conducted using a WindCube v2.1 lidar, referred to as the mobile lidar, mounted on a hexapod to simulate buoy motion, with a fixed lidar used as a reference. To assess the motion-induced effects on turbulent velocity fluctuations measured by floating lidar systems, the root-mean-square error (RMSE) of LOS velocity fluctuations obtained from the fixed and mobile lidars was calculated. A comprehensive wind dataset spanning 45 hours was analyzed, with a focus on regular motions involving single-axis rotations and combinations of rotations around multiple axes. The investigation of single-axis rotations revealed that the primary influencing factor on the results was the alignment between wind direction and the axis of rotation. The highest RMSE values occurred when winds propagated perpendicular to the rotation axis, resulting in pitch motion, whereas the lowest RMSE values were observed when wind propagated along the rotation axis, leading to roll motion. Furthermore, yaw motion was found to increase the RMSE compared to scenarios without yaw motion. Moreover, the addition of motion around extra axes of rotation was found to increase RMSE. High wind speed emerged as a significant driver of RMSE, with higher velocities leading to higher RMSE values. The study also indicated that the role of wind shear in influencing RMSE of LOS velocity fluctuations requires further investigation. Additionally, the study explored the impact of motion period, revealing that motion frequencies affect the LOS velocity spectra within the expected inertial sub-range. However, the impact on RMSE was found to be limited in comparison to the amplitude, wind direction, and wind speed.

Nicolas Thebault et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2023-126', Anonymous Referee #1, 08 Oct 2023
  • RC2: 'Comment on wes-2023-126', Anonymous Referee #2, 14 Oct 2023

Nicolas Thebault et al.

Nicolas Thebault et al.


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Short summary
This study examines motion's impact on LOS turbulent velocity fluctuations measured by lidar profilers. Onshore tests used a mobile lidar (WindCube v2.1) on a hexapod, comparing it to a fixed lidar. RMSE was calculated to assess motion effects on turbulence. Results showed alignment, wind speed and amplitude as significant influences on RMSE. Motion frequency affected LOS velocity spectra but had limited impact on RMSE compared to other factors.