## 3 Test and Results
### Results  
Acquisitions corresponding to operating condition c (rotor blades motionless, no action of the wind) were used to obtain the mean value of the horizontal distance from TLS. For a point P on the wind tower located at H = 65 m height from the tower base, the mean ground distance of D = 47.293 m was \begin{table}
\begin{tabular}{c c c c c} \hline
**Operating Condition** & **Initial Timestamp** & **Final Timestamp** & **Initial Time (CET)** & **Final Time (CET)** \\ \hline a & 408.67 & 430.35 & 13.37.50 & 13.38.12 \\ a & 664.55 & 678.75 & 13.41.57 & 13.42.11 \\ a & 736.23 & 754.69 & 13.43.08 & 13.43.27 \\ b & 766.81 & 846.19 & 13.43.39 & 13.44.59 \\ c & 888.28 & 917.17 & 13.45.41 & 13.46.10 \\ d & 937.18 & 1054.41 & 13.46.29 & 13.48.27 \\ a & 643.17 & 708.68 & 14.00.00 & 14.01.06 \\ \hline \end{tabular}
\end{table} 
Table 3: TLS sampling periods. obtained. The procedure described in the Section 2.3.2 was applied. The comparison between raw data and the values obtained by the procedure can be observed in Figure 8.  
Figure 8: **(a)** Distance DP,TLS of point P on the wind tower located at H = 65 m during acquisition in operating condition c (see Table 3); **(b)** result after applying the proposed methodology; **(c)** frequency distribution of differences between modelled DP,TLS distances (blue dots) and moving average (red line). The standard difference between measured and model DP,TLS distances is 0.6 mm. The time series of TLS distances of point P, located at the top of the wind tower, is plotted in panel 8(a). Panel 8(b) displays the results obtained by applying the procedure in Section 2.3.2 to the detrended measurements of Panel 8(a). Results provided by the proposed methodology and the mean curve obtained by applying a moving average operator are plotted in Figure 8b, while the frequency distribution of their differences is plotted in Figure 8c. The standard deviation of this frequency distribution provides the precision of TLS estimates of distances equal to 0.6 mm. Figure 9 shows the plot of TLS ground distances vs. timestamps of four points P on the wind tower located at different heights above the base, obtained by the proposed procedure. Data were collected from 13.41.57 till 13.42.11 CET. These results were obtained in condition a (see Table 3) with a fully operational wind turbine. The peak-to-peak amplitude of oscillations decreased from 15 mm to 2 mm when moving from H = 60 m to H = 15 m on the wind tower. Figure 10 shows the plot of TLS ground distances vs. timestamps of a point P on the wind tower located at H = 60 m above the base. Data were collected from 13.43.39 till 13.44.59 CET. These results were obtained in condition b (see Table 3) with the wind turbine in deactivation mode. Damped oscillations had an amplitude decreasing from 90 mm to a few mm. The average ground distance from the TLS increased and tended to stabilize around a value of 47.293 m.  
The corresponding spectrum of vibration frequencies are shown in Figure 11a,b, along with the spectrum obtained for data collected during the stop of the wind turbine in Figure 11c,d. In both cases, two peaks are observed at 0.4 Hz and 40 Hz. Figure 9: Ground distances from TLS of points at a height of 60 m (d\({}_{60}\) line), 40 m (d\({}_{40}\) line), 25 m (d\({}_{25}\) line) and 15 m (d\({}_{15}\) line) on the tower base. Abscissae are the timestamps in sec. The wind turbine is fully operational. Figure 12 shows the spectrum of vibration frequencies for a point P on the wind tower located at H = 25 m above the base, obtained for data collected during the deactivation of the wind turbine. Additionally, in this case, two peaks can be observed at 0.4 Hz and 40 Hz. Figure 11: Spectra of vibration frequencies of point P on the wind tower located at H = 60 m. Spectrum for the data collected during the deactivation of the wind turbine (**a**). Enlargement of the low frequencies (**b**). Spectrum for the data collected during the stop of the wind turbine (**c**). Enlargement of the low frequencies (**d**).