Turbulence measurement with a two-beam nacelle lidar

The analysis of the turbulence intensity measurement is performed for a lidar measuring horizontally with two beams. First the turbulence intensity measured by such a system was evaluated theoretically. The Mann model of turbulence was used to evaluate the true value of the turbulence intensity of the wind speed and the main effects of the lidar measurement principles on turbulence intensity measurement were modeled: - A lidar senses the wind speed over the probe volume acting as a low pass-filter and thus cannot resolve high frequency turbulence; - The horizontal wind speed is retrieved from the combination of the radial speeds measured along two line-of-sights with different orientations; this results in the contamination of the lidar turbulence intensity measurement from the transverse component of the wind field.

Secondly, the theoretical results were compared to experimental measurements. A two-beam nacelle lidar was placed on a platform at 60m height inside a lattice meteorological mast. The lidar was measuring forward at a range of 80 m. The turbulence intensity measured by the lidar was compared to that measured by the cup anemometer placed on a boom at the same height as the lidar and on the same met mast.