Apparent wind in knots and degrees. Note that a number of additional factors come into play when converting the measurements from the masthead anemometer into the true wind if a high degree of accuracy is required, including the following: In the presence of a current, the true wind is considered to be that measured on the craft drifting with the water over the bottom, and wind with respect to the sea bed as the "ground" or "geographical wind". The apparent wind on board (a boat) is often quoted as a speed measured by a masthead transducer containing an anemometer and wind vane
Wind resource assessment be recorded for at least one year to calculate an annually representative wind speed frequency distribution. Since onsite measurements are usually only available for a short period, data is also collected from nearby long-term reference stations (usually at airports). This data is used to adjust the onsite measured data so that the mean wind speeds are representative of a long-term period for which onsite measurements are not available. Versions of these maps can be seen and used with software applications such as windNavigator. The following calculations are needed to accurately estimate the energy production of a proposed wind farm project: