Mid frequency shallow water fine-grained sediment attenuation measurements

Area of Science:

• Acoustic oceanography
• Geophysics
• Marine sedimentology

Background:

• Sediment acoustic attenuation is vital for sonar prediction but difficult to measure accurately.
• Existing measurement techniques have limitations, including frequency gaps and biases in fine-grained sediments.
• A notable frequency gap exists between 600-4000 Hz for sediment attenuation measurements.

Purpose of the Study:

• To explore a novel shallow water measurement technique for sediment acoustic attenuation using long-range reverberation.
• To address the challenges and biases associated with historical sediment attenuation measurements.
• To investigate the sensitivity of reverberation to depth-integrated attenuation in fine-grained sediments.

Main Methods:

• Developed an approximate solution using energy flux theory to analyze reverberation data.
• Employed Bayesian methods for simulation to validate the theoretical model.
• Conducted reverberation measurements over a 10m fine-grained sediment layer in shallow water.

Main Results:

• The energy flux theory demonstrated high sensitivity of reverberation to depth-integrated attenuation.
• Bayesian simulations confirmed the theoretical predictions.
• Measured sediment attenuation was 0.009 dB/m/kHz (95% CI: 0.006-0.013 dB/m/kHz), among the lowest reported for shallow water fine-grained sediments.

Conclusions:

• The long-range reverberation technique is effective for measuring acoustic attenuation in shallow water fine-grained sediments.
• This method provides accurate attenuation values, filling a critical measurement gap.
• The findings contribute to improved predictions of sonar performance in shallow marine environments.