INSTRUMENTATION IN WIND RESOURCE ASSESSMENTKeywords: Wind Resource Assessment (WRA), Wind mast, Wind is an intermittent resource. Wind resource assessment is necessary to define the most suitable wind turbine given the local meteorology, the layout of the wind farm and to calculate the expected energy production of the wind farm. Wind parameters are scanned at regular time intervals and the data points are averaged by a data logger mounted on the wind mast. Wind speed, wind direction, wind shear, wind turbulence, air density, air temperature, atmospheric pressure, solar radiation, relative humidity, rainfall pattern are few variables to be monitored. These variables are usually measured installing one or more meteorological masts in the area where the wind farm is planned. This activity is called “site measurement campaign”. The traditional method for accredited measurements for wind energy is to mount calibrated cup anemometers on tall wind masts. The wind mast (met mast) is a tower made of steel (or, more unusually, concrete) where the measuring equipments are installed. Ideally the met mast should have the same height of the wind turbines that are going to be installed in the area.Some typical equipments mounted on a wind mast are : EquipmentSignificanceWind VaneTo identify the wind directionAnemometerTo measure wind speedPyranometerTo measure solar radiationAmbient temperature sensorTo measure temperatureBarometric Pressure sensorTo measure atmospheric pressureRelative humidity sensorTo measure relative humidityData loggerTo record the data in digital formSome key parameters of manufacturer’s specifications which help in evaluating the meteorological sensors are :Accuracy and ResolutionDurabilityOperating temperatureResponse timeTime interval of recording dataCompatibility to data logger and deploymentCompatibility of software for analyzing the data Power backupTechnical lifetimeWind turbines are being installed at an ever increasing rate today, on and offshore, in hilly and forested areas and in complex mountainous terrain. At the same time, as the wind turbines become bigger and bigger, they reach higher and higher into the atmosphere but also into hitherto unknown wind and turbulence regimes. As turbines grow in height, high meteorology masts and instrumentation becomes more and more cumbersome and expensive correspondingly. Costs for installation of tall instrumented met towers increase approximately with mast height to the third power and licensing permits can be time consuming to obtain. With hub heights above 100 m and rotor planes nowadays reaching diameters of 120 m or more on today’s 5 MW turbines, the wind speed distribution over the rotor planes will no longer be representatively measured from a single hub height measurement point, but will also require a multi-height measurement strategy with measurements ranging in heights between 50–200 m, for the purpose of capturing the simultaneous wind distribution over the entire wind turbine rotor.