2-2. Underwater soundscape analysis
All data processing, analysis, and visualization were conducted using
MATLAB 2021a (Mathworks, Inc.). The underwater soundscape was analyzed
in the time-averaged spectrum levels and spectrograms. The spectrum
levels were estimated by the power spectral density (PSD) in units of dB
re 1 \(\mu\)Pa2/Hz (Han et al., 2021), which was
computed from 1 minute of acoustic data with a 1-sec Hanning window,
50% overlap and a fast Fourier transform length of 96,000 points. The
spectral probability density, which represents percentile spectra
(Merchant et al., 2013), was then calculated to evaluate temporal
variations in the sound pressure levels and the impact of leopard seal
vocalizations on the underwater soundscape in the measurement region.
The spectrogram was represented by stacking the intensity-averaged PSD
in 10-minute intervals, as that depicted by higher temporal resolution
was ineffective to show acoustic events over time.