## 4 Results
### Correlation Between Operational Parameters and Acoustic Emission Data  
#### 4.2.1 Wind Speed and Temperature  
Figure 9 illustrates the correlations between the acoustic emission parameters and wind speed. To emphasize the relationships among the values depicted in the correlation diagrams, moving averages for the maxima were inserted as black lines. These moving averages were computed using a window width of 1000 samples, and a minimum of 200 values was set to ensure the capture of the trend at the beginning of the curve. Consequently, the correlation becomes particularly clear in the plot of the amplitude of sensor 7. At low wind speeds (<1 m/s), the amplitudes remain low but gradually increase with increasing wind speed. The spread of the maxima shows significant variability up to a wind speed of approximately 7 m/s, after which it abruptly narrows to \(\pm\)2 dB. At this point, sensor 7 registers the highest operational noise level. Similar observations have already been made in [44], highlighting a substantial increase in acoustic emission intensity up to wind speeds of 7-8 m/s. On average, the amplitude at sensor 7 increased by approximately 20 dB.  
The moving average reveals a qualitatively similar trend in other plots. Sensor 3 shows high similarity in both amplitude and energy but with a generally higher operational noise level. Moreover, the amplitude differences between wind speeds of 1 and 7 m/s are less pronounced when compared to sensor 7, with a 6 dB increase at sensor 3.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Structural** & **Sensors** & **Feature** & **Q0.1** & **Q0.9** \\
**Component** & **Evaluated** & & & \\ \hline \multirow{4}{*}{Foundation} & \multirow{4}{*}{7} & A [dB] & - & 91.5 \\  & & E [eu] & - & \(1.71\times 10^{7}\) \\ \cline{3-5}  & & SC [kHz] & 19.5 & - \\ \cline{3-5}  & & A [dB] & - & 106.9 \\ \cline{3-5}  & & E [eu] & - & \(1.22\times 10^{10}\) \\ \cline{3-5}  & & SC [kHz] & 21.5 & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Statistical parameters for operational noise at the transition piece and the foundation (sensors 3 and 7) for the signal features amplitude in decibels, energy in an engineering unit, and spectral centroid in kilohertz representing the evaluation threshold for the PoD model.  
In the spectral domain, a noticeable increase in frequency begins at a wind speed of approximately 1 m/s. At around 3.5 m/s, this increase stabilizes, reaching a plateau of around 27.3 kHz at sensor 3 and 23.9 kHz at sensor 7. Notably, there is an accumulation of minima at sensor 3 within the wind speed range of 2.3 to 5.5 m/s. Despite an analysis of operational parameters, no specific grouping could be identified, suggesting that unrecorded parameters may additionally influence background noise. Consequently, individual effects cannot be conclusively and distinctly isolated.  
The impact of temperature is not illustrated, as there was no apparent correlation between temperature and ambient noise level. The relationship seemed entirely random at sensor 3 (transition piece). Sensor 7 (foundation) exhibited occasional instances of larger peak amplitudes and energies at temperatures ranging between 10 and 25. However, no significant correlation was evident. The possibility of a connection with maintenance interventions can be excluded, as these periods were previously filtered from the analysis, as noted earlier.