Assessing Lidar for Measuring Atmospheric Turbulence
Researchers deployed multiple lidars at the Atmospheric Radiation Measurement Southern Great Plains atmospheric observatory to explore different strategies for measuring atmospheric turbulence at wind turbine hub heights.
For planning purposes, wind energy providers need accurate assessments of wind resources available at a given site. Such assessments require estimates of wind speeds and turbulence at the height of a turbine rotor disk, 40 to 120 meters above the ground. Traditionally, these measurements have been made with cup anemometers on tall meteorological towers. However, as wind turbines grow taller, building meteorological towers that reach these heights has become more difficult and costly. In response, scientists are exploring the use of remote-sensing devices (e.g., Doppler lidar) to assess wind resources. In this study, scientists explored the use of two different multi-lidar scanning strategies, known as the tri-Doppler technique and virtual tower technique, for measuring atmospheric turbulence.
Results indicate that the tri-Doppler technique measures higher values of horizontal turbulence than the WindCube lidar under stable atmospheric conditions, reduces variance contamination under unstable conditions, and can measure high-resolution profiles of mean wind speed and direction. The virtual tower technique provides adequate turbulence information under stable conditions but cannot capture the full temporal variability of turbulence experienced under unstable conditions because of the time needed to readjust the scans.
To evaluate the ability of multi-lidar scanning strategies to measure wind speeds and three-dimensional turbulence, three scanning lidars and a vertically profiling WindCube lidar were operated during the summer of 2013 at the Southern Great Plains Atmospheric Radiation Measurement (ARM) Climate Research Facility site, a field measurement site located in northern Oklahoma and instrumented with various in situ and remote-sensing devices. This work marks the first time the tri-Doppler and virtual tower techniques have been evaluated under vastly different stability conditions at the same site and compared with measurements from a commercially available lidar. The evaluation of both techniques at the same site enables comparison of the techniques under similar atmospheric conditions while utilizing the same scanning lidars for both techniques. Comparisons with data obtained from a commercially available lidar are extremely valuable, as they directly indicate any advantage of using a multi-lidar scanning technique as opposed to a single commercially available lidar.
National Wind Technology Center, National Renewable Energy Laboratory
Data were obtained from the Atmospheric Radiation Measurement Climate Research Facility, a U.S. Department of Energy Office of Science user facility sponsored by the Office of Biological and Environmental Research. J. F.N. and S.W. received funding from Laboratory Directed Research and Development award 12-ERD-069 from Lawrence Livermore National Laboratory.
Newman, J. F., T. A. Bonin, P. M. Klein, S. Wharton, and R. K. Newsom. 2016. “Testing and Validation of Multi-Lidar Scanning Strategies for Wind Energy Applications,” Wind Energy 19(12), 2239-254. DOI: 10.1002/we.1978.