Presentations

Abstract

Doppler Wind Lidars are an important measurement technology in the wind industry for applications such as energy yield assessments, power performance measurements, or as a permanent wind measurement on operational sites. The increasing number of global wind Lidar deployments provides the means to assess Doppler wind Lidar performance under different environmental conditions, and specifically in extremely low aerosol atmospheres. Doppler Wind Lidars operate by transmitting a laser signal and measuring the light scattered by particles carried by the wind. This Doppler shift provides the wind velocity along the line-of-sight. The intensity of this backscattered light is a function of the intensity of the incident light and scatterer density. There are two fundamental types of Wind Doppler Lidars: Continuous-wave (CW) and Pulsed Lidars. Both these technologies are widely used for wind measurement applications, and offer value to accelerate project development, reduce energy yield assessment uncertainties and provide measurements in remote locations. The measurement principles of these systems vary. CW Lidars operate by focusing the laser power at each measurement height in sequence, in contrast pulsed Lidars use a range gating principle (time of flight) to determine the measurement height where the available laser signal is dispersed across multiple range gates. This difference in measurement principles may lead to a variation in performance in low aerosol concentration environments, where there are fewer particles in the atmosphere to result in a return signal to the Lidar. Here we describe an investigation into the availability of wind speed measurement data in the clear-air, low-backscatter conditions of Finland and in the European Alps. These conditions may be similar to other high latitudes (such as Scandinavia, Northern Canada) and high altitudes (Rocky Mountains of the USA). Equally, very cold atmospheres are often associated with low aerosol concentration because airborne water molecules (one of the main aerosols responsible for backscattering the emitted signal) will be frozen out of the air. A concurrent measurement campaign was conducted over a period significant period for a Developer using a CW Lidar and a Pulsed Lidar on a Finnish development project and on an Austrian wind project. This poster examines the performance of each system (including data availability) under different environmental conditions and the implications with regards a bankable energy yield assessment.