The calibration of the two lidars of the UniTTe project is ongoing (WP2). It started early November 2014 and will continue until the end of April 2015. The existing calibration procedure for 2-beam lidars (Courtney M.: “Calibrating nacelle lidars”, (2013), DTU Wind Energy E-0020) has been adapted for both the 5-beam Demonstrator (Avent Lidar) and the ZephIR Dual-Mode (Zephirlidar). The calibration of both systems is taking place at DTU test station for large wind turbines, Høvsøre, in Jutland.
1. Calibration of the radial wind speed
1.1. Procedures
The main steps of the calibration procedures are:
• Geometry verification: the opening angle(s) between beams are measured in order to verify it corresponds to the specifications.
• Inclinometers calibration: since the lidars are on the ground, the beam is slightly tilted upwards so that it passes close by a mast top-mounted reference anemometer. Hence the need for calibrating the internal inclinometers.
• Measurement campaign: data are collected over a period of time in order to obtain the formal calibration relation between the lidar line-of-sight velocity and the measurements taken by the reference instruments.
1.2. Measurement campaign set up
The 5-beam Demonstrator has been measuring in Høvsøre since November 2014. The 5 beams of the pulsed lidar are being calibrated successively over about a month each. The ZephIR DM has been installed early February 2015. ZephIR DM is a continuous wave lidar featuring one scanning beam and therefore requires only one measurement period.
Both lidars are steering their beam towards two 9-meter tall masts instrumented with a cup and a sonic anemometer, respectively for measuring horizontal wind speed and direction. The distance between the lidars and the masts is 260m.
2. Outcome and deliverables
The performed measurements will provide the calibration relation between the lidars and the reference instruments as well as a comprehensive uncertainty budget. The calibrated lidars will then be ready for being installed on the nacelle of a Siemens 2.3 MW turbine in Nørrekær Enge for a measurement campaign in flat terrain.
Two calibration reports will be written and a paper on ‘Calibration procedures for nacelle-mounted profiling lidars’ will be published. This work will also be presented at the next DEWEK conference in Bremen on the 20th of June 2015.