Wind is usually measured by its speed and direction. Wind atlases show the distribution of wind speeds on a broad scale, giving a graphical representation of mean wind speed (for a specified height) across an area. They are compiled by local meteorological station measurements or other wind-related recorded data.
Traditionally, wind speed is measured by anemometers – usually three cups that capture the wind rotating around a vertical axis (pictured below). The wind direction is measured with weather vanes.
After measuring wind data for at least one year, the mean annual wind speed can be calculated. Wind speed and wind direction statistics are visualised in a wind rose, showing the statistical repartition of wind speed per direction.
Wind statistics show the best sites to locate wind farms according to the best wind resources. They also provide further information on how the turbines should be positioned in relation to each other and what the distance between the turbines should be.