Fig. 4

a Typical spectrograms of the stacked waveform for the input signal. b Typical spectrograms of the raw waveform (left) and the stacked waveform (right) for the most distant receiver, AC4, under dry conditions
a Typical spectrograms of the stacked waveform for the input signal. b Typical spectrograms of the raw waveform (left) and the stacked waveform (right) for the most distant receiver, AC4, under dry conditions