Fig. 5: Noise levels.
a Long-term spectrogram of acoustic data recorded in Bahía Norte from November 19, 2018 to October 3, 2020, as well as sound energy in frequency bands representative of b low-frequency vessel noise (nominal 125 Hz third-octave band) and c high-frequency signals including UA devices and echosounders transmitting at 28 kHz and 50 kHz. The minimum noise floor for the c measurements (~40 dB re: 1 µPa2/Hz) was determined by electronic self-noise produced by the acoustic recording system and was not a reflection of the true minimum ambient noise levels.
