Preprints
https://doi.org/10.5194/wes-2021-62
https://doi.org/10.5194/wes-2021-62

  16 Aug 2021

16 Aug 2021

Review status: this preprint is currently under review for the journal WES.

Alignment of scanning lidars in offshore wind farms

Andreas Rott1, Jörge Schneemann1, Frauke Theuer1, Juan José Trujillo Quintero2, and Martin Kühn1 Andreas Rott et al.
  • 1ForWind, Institute of Physics, Carl von Ossietzky University Oldenburg, Küpkersweg 70, 26129 Oldenburg, Germany
  • 2UL International GmbH, Kasinoplatz 3, 26122 Oldenburg, Germany

Abstract. Long-range Doppler wind lidars are applied more and more for high resolution areal measurements in and around wind farms. Proper alignment, or at least knowledge on how the systems are aligned, is of great relevance here. The paper describes in detail two methods that allow a very accurate alignment of a long-range scanning lidar without the use of extra equipment or sensors. The well-known so-called Hard Targeting allows a very precise positioning and north alignment of the lidar using the known positions of the surrounding obstacles, e.g. wind turbine towers. Considering multiple hard targets instead of only one with a given position in an optimization algorithm allows to increase the position information of the lidar device and minimizes the consequences of using erroneous input data. The method, referred to as Sea Surface Leveling, determines the leveling of the device during offshore campaigns in terms of roll and pitch angle based on distance measurements to the water surface. This is particularly well suited during the installation of the systems to minimize alignment error from the start, but it can also be used remotely during the measurement campaign for verification purposes. We applied and validated these methods to data of an offshore measurement campaign, where a commercial long-range scanning lidar was installed on the transition piece platform of a wind turbine. In addition, we present a model that estimates the quasi-static inclination of the device due to the thrust loading of the wind turbine at different operating conditions. The results show reliable outcomes with a very high accuracy in the range of 0.02° in determining the leveling. The importance of the exact alignment as well as the possible applications are discussed in this paper. In conclusion, these methods are useful tools that can be applied without extra effort and contribute significantly to the quality of successful measurement campaigns.

Andreas Rott 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-2021-62', Anonymous Referee #1, 15 Sep 2021
  • RC2: 'Comment on wes-2021-62', Anonymous Referee #2, 04 Oct 2021

Andreas Rott et al.

Andreas Rott et al.

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Short summary
We present three methods that can determine the alignment of a lidar placed on the transition piece of an offshore wind turbine based on measurements with the instrument. A practical implementation of hard targeting for north alignment, a method called Sea Surface Leveling to determine the leveling of the system from water surface measurements and a model that can determine the dynamic leveling based on the operating status of the wind turbine.