than 12,000 rms characteristic values and 150 spectra were available from each unit.The average wind speed over a period of 10 min measured with an ultrasonic anemometer located on the nacelle roof is available from the SCADA data set. As an example, the wind conditions during 19 days have been plotted in Fig. 2 for four units. Because the measured wind conditions are very similar in terms of magnitudes and trends for all of them during the period of interest, it is assumed that the vibration behavior of all the units can be compared.