Posters

Abstract

Floating lidar systems (FLS) represent an efficient and easily deployable tool to conduct wind resource assessments for offshore wind farms. Its ease of installation, capability of measuring at multiple altitudes, and ease of collective installation around the desired area make it a convenient, and at times cheaper, alternative to a meteorological mast. As these measurements are made on a moving buoy, however, the vertical lines of sight are influenced thus impacting wind flow pattern measurements on the horizontal wind speed and turbulence intensity. Lidars are already known to have additional uncertainty attributed to inter-beam filtering due to volumetric averaging in wind speed reconstruction; adding motion only adds to the uncertainty. A solution to reduce this uncertainty and better capture turbulent structures is to increase the sampling rate of the lidar. This research presents a study that demonstrates the benefits of an FLS with a higher sampling rate. The project consists of comparing two floating lidar systems (FLS) against a met mast: one FLS measuring in 1Hz, and the other in 5Hz. The two-week dataset is composed of 10-minute averaged horizontal wind speed (HWS), standard deviation of wind speed, and turbulence intensity (TI) data from the two FLSs and met mast ultrasonic anemometers at 51m, 71m, and 91m. Only yaw movement was compensated on the FLS dataset. The results demonstrate a notable improvement in bias and correlation from 1Hz to 5Hz FLS measurements against the reference for HWS, standard deviation of HWS, and TI. For HWS, the bias (at all heights) between the met mast and FLS measuring at 1Hz was 0.09 m/s and was decreased to -0.005 m/s with 5Hz measurements. TI 1Hz biases were 6% and reduced to 4% with 5Hz measurements, with a 12% increase in R2 correlation (0.39 to 0.44). The standard deviation of HWS was also significantly improved with 5Hz measurements, decreasing the bias against the reference from 0.5 m/s with 1Hz measurements to 0.29 m/s and a 6% increase in correlation (0.63 to 0.67). Regarding bias/deviation/slope differences by heights, no notable change was seen for all variables. The general results of this study show promising results of using higher frequency data acquisition for offshore FLS measurements, thus paving the way for longer campaigns to assess concrete improvement and performance in more varied offshore conditions.