Advance measurement of gusts by laser anemometry

A coherent laser radar (or Doppler lidar) operating at a wavelength of 1.55 μm has been mounted on the nacelle of a 2.3 MW wind turbine in order to measure the wind speed in front of the blades at ranges up to 200 m. The lidar measures the component of wind speed along its beam direction but, since it rotates with the nacelle to point into the wind, this component normally differs negligibly from the actual wind speed. As an example to demonstrate the lidar's capabilities, we present samples of wind data gathered over an 18 h period in March 2003, illustrating the development of gusts that appears to be associated with the onset of solar ground heating. Wind speeds over the full period lay in the range 4–10 m s−1, and the gusts were evident as a near-discontinuity in wind speed typically of order 1–2 m s−1, but reaching values larger than 3 m s−1. The typical timescale between gusts was of order 1 min. Improvements to this experiment are proposed that will provide more detailed information on spatial and temporal structure of such gusts.