This part of IEC 61400 presents measurement methods that enable noise emissions of a wind turbine to be characterised. This involves using measurement methods appropriate to noise emission assessment at locations close to the wind turbines, in order to avoid errors due to sound propagation, but far away enough to allow for the wind turbine to be regarded as finite source. The methods described are different in some respects from those that would be adopted for noise assessment in community noise studies. They are intended to facilitate characterisation of wind turbine noise emissions with respect to a range of wind speeds and directions. Standardisation of measurement methods will also facilitate comparisons between different wind turbines. The methods present methodologies that will enable the noise emissions of a single wind turbine to be characterised in a consistent and accurate manner. These methods include the following: - location of acoustic measurement positions; - requirements for the acquisition of acoustic, meteorological, and associated wind turbine operational data; - analysis of the data obtained and the content for the data report and - definition of specific acoustic emission parameters, and associated descriptors which are used for making environmental assessments. This International Standard is not restricted to wind turbines of a particular size or type. The methods described in this standard allow for the thorough description of the noise emission from a wind turbine. A method for small wind turbines is described in Annex F.