Issue 78

C. Vendittozzi et alii, Fracture and Structural Integrity, 78 (2026) 519-540; DOI: 10.3221/IGF-ESIS.78.30

Figure 9: Dataset B: Multitaper time–frequency maps (DPSS; NW=3, K=5) for sensors (a) S3 and (b) S4. Spectrograms computed with a Thomson multitaper estimate using the same frame length and hop as the Hann STFT (L=2048 samples, H=512 samples). Narrowband frequency families are visible within the analyzed record and change in prominence around the FBG-derived event-centered windows.

Figure 10: Dataset A: Hann STFT spectrograms for sensors (a) S3 and (b) S4 (L=2048 samples, H=512 samples, same frame length and hop as the multitaper maps). Compared with multitaper estimates (Fig. 8), the single-taper STFT exhibits higher background variability under the same segmentation and frequency band.

Figure 11: Dataset B: Hann STFT spectrograms for sensors (a) S3 and (b) S4 (L=2048 samples, H=512 samples, same frame length and hop as the multitaper maps). Compared with multitaper estimates (Fig. 9), the single-taper STFT exhibits higher background variability under the same segmentation and frequency band. Ridge families as compact descriptors and dataset-to-dataset comparison To obtain compact event-level descriptors, ridge trajectories were extracted from the multitaper spectrograms by selecting, at each accepted time frame, the frequency bin of maximum spectral power within the 9–500 Hz analysis band, after

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