2.2.1. Peak Picking Method Based on the Correlation Analysis (PP-CA)

Ambient vibration responses to the (assumed) white noise signal are considered in the PP-CA method. The method is based on the correlation analysis of response signals in the frequency domain. This was proposed in [9] as the first OMA technique. Auto- and cross-correlation functions, determined for different measuring points together with the coherence functions, allow us to identify natural frequencies, as briefly described in [10]. Additional study of the phase shifts allows us to determine mode shapes. The damping ratios cannot be identified, which is the method's limitation. The practical applications of the PP-CA technique are addressed in, e.g., [11–13].

**Figure 2.** Measuring points' locations (P1–P10) and directions *x* and *y* of measurements (sensors 1 and 2).

**Figure 3.** Situation plan.
