Fig. 10

Multi-camera recording of three Asian elephants. Determination of vocalizing elephant with Eulerian video magnification. a–d Corresponding images from video recordings from CAM 1 (a), CAM 2 (b), CAM 3 (c), and CAM 4 (d). Image probes for vibration analysis are indicated on images and labeled in a. e–v Analysis of vibrations at different body positions of the three elephants during the video capture. The audio spectrograms associated with each recording are displayed at the top (e, j, o, and r), and the durations of the two vocalization events (events 3 and 4 in Fig. 9) are highlighted with dashed lines. Plots of normalized pixel intensity (NI) over time for image probes placed on the male head (f, k, and s), the male posterior (h, m, p, and u), the female 1 and female 2 posterior (i, n, q, and v) reveal periods with large amplitude vibrations relative to background noise on the surface of the male. The male head was not available for analysis in the video capture by CAM 3 due to the angle of the elephant. By performing a short-time Fourier transform (6-bit window) of the male head signal, vibration spectrograms were generated from the different recordings (g, l, and t) showing a good match with audio spectrograms (e, j, and r)