In a standard wind farm, 3 different Meteorological Tower (known as Met Mast) are installed.
First of all, a tower is needed to provide several years (normally at least 2) of wind data. This tower is used to collect not only wind data, but also other information such as temperature, humidity, rain and so on.
Normally these towers are lower that the WTGs that will be installed on site, with an average height of 40 meters: the wind speed at the hub height will be interpolated at the correct elevation using one of the available formulas.
If after a deep study of the energy that can be provided by the wind a promising location is found and the wind farm construction start, one or more temporary met mast are erected.
This towers measures the actual wind speed in the positions where a WTG will be erected, at the hub height (80 meters or more) and are used to calibrate the power curve, that is if the produced energy is in line with the expected values.
After a couple of weeks (normally 2 months) this tower is removed and a turbine is installed nearby.
The third tower is the wind farm tower: this tower will be used to transmit to the control centre the meteorological situation in the location and it has a paramount importance for the management of the site. It normally has the same height of the turbines of the wind farm.