Spatial Variability of Marine Winds as studied by Doppler Lidar

Accurate, high-resolution vertical profiles of the horizontal wind and other wind information in the lowest several hundred meters of the atmosphere are essential for many applications, such as transport of air pollutants and other airborne trace species, numerical model verification and improvement, research into meteorological factors affecting the flows over the ocean, and more recently, offshore wind energy. Because information is difficult to obtain above the surface, users will have to rely on remote sensing systems, such as Doppler lidar, to obtain the needed data. Many significant challenges are involved in obtaining accurate wind data over the sea from moving platforms, such as removing the various motions of the platform from the wind estimates. ESRL has adapted its scanning, pulsed, coherent Doppler lidar system, the High Resolution Doppler Lidar (HRDL) to operate from a moving ship by developing a sophisticated motion compensation system that allows the winds to be measured to high accuracy. The paper will descript the measurement system and present results related to wind energy issues such as temporal and spatial variability of marine winds, distributions of wind speed and wind direction at the heights of modern turbine rotors. Presented wind flow characteristics were obtained off the New England coast, when HRDL was deployed on the research vessel Ronald Brown. This datasets was chosen because the waters off the New England coast is the region planned for development of wind farms in the near future. Analysis of wind and turbulence characteristics over a wide range of heights, variations of wind shear in time during strong and calm wind nights, along with examples of error in the actual and predicted wind resources will be given. These results will illustrate of the kind of information available from remote sensing instruments for wind energy research and show the value of the existing offshore datasets to gain greater insight into the characteristics of offshore flows at turbine heights for better understanding of the range of marine atmospheric conditions.