Statistical characterization of low-frequency seabed ambient noise on the southwest Indian ridge based on passive...

The Yuhuang-1 Hydrothermal Field (YHF) on the Southwest Indian Ridge (SWIR) is known for its polymetallic sulfide resources. We deployed a passive acoustic recorder to quantify the spectral-temporal characteristics of ambient noise within this area. Hence, the resulting dataset will provide fundamental data for forthcoming seabed environmental assessments mandated under prospective deep-sea mining licensing regimes. This study investigates noise spectral level distribution in YHF using passive acoustic recorder. During the measurement period, the presence of the remotely operated vehicle (ROV) and vessel were near the recorder, causing significant low-frequency noise pollution. To address this, sound pressure data were analyzed using Welch's method, with notch filtering applied to reduce noise pollution and remove streaks from the noise spectrogram. The results indicate that the median noise spectral level decreases with increasing frequency below 50 Hz. Below 500 Hz the noise spectral level distribution with the highest probability density is close to the median. Additionally, the seabed ambient noise spectral levels (SANSL) under different wind speed categories decrease with increasing frequency. The Pearson correlation coefficient between SANSL and wind speed increases with frequency, showing a notable correlation within the 300-500 Hz frequency range. It was also observed that equipment such as ROVs can enhance SANSL by approximately 20 dB. To accurately reflect the original ambient noise characteristics, noise reduction processing based on the spectral characteristics of strong noise pollution sources is essential. This study provides valuable insights and serves as a reference for future research on the distribution characteristics of SANSL in the YHF.