Lidar Simulations to Study Measurements of Turbulence in Different Atmospheric Conditions

Modern lidar technology promises a fundamental enhancement of wind velocity measurements for site assessment. Previous studies have shown good agreements between lidars and mast mounted sonic anemometers concerning measurements of the 10 minute average horizontal wind velocity in flat terrain but have shown substantial differences concerning the measurement of turbulence intensity. One of the main reasons for poor turbulence measurements is assumed to lie in the scanning technique called VAD, applied by lidars. In contrast to a sonic anemometer, a VAD-scanning lidar senses the wind field at different positions along a circle. This is centred at the target point, and with a radius three orders of magnitude larger than the typical size of an anemometer. The resulting temporal and spatial averaging by the VAD scan influences the turbulence measurements. To understand the effects of different VAD scanning configurations and of the atmospheric condition on measuring turbulence, a numerical lidar scanner simulator was used. The influence of the VAD cone angle and the stability of the used LES generated wind fields were studied. The results show a high dependency on the used cone angle and the atmospheric stability.