Marine compressed air source array acoustic field characterization from at-sea measurements: Long-range propagationa)

Area of Science:

• Oceanography
• Marine acoustics
• Seismic exploration

Background:

• Marine seismic surveys use compressed-air arrays, generating significant acoustic energy.
• Understanding long-range acoustic propagation is crucial for environmental impact assessments and geophysical surveys.

Purpose of the Study:

• To measure the three-dimensional acoustic field of a marine seismic source array.
• To analyze long-range acoustic propagation characteristics, including received sound pressure and sound exposure levels (SELs).
• To investigate the influence of receiver depth, array orientation, and propagation conditions on acoustic signals.

Main Methods:

• Conducted a comprehensive experiment in the northern Gulf of Mexico in 2007.
• Measured acoustic fields using a standard marine compressed-air source array.
• Collected data on received sound pressure levels and SELs at various ranges and depths.

Main Results:

• Received peak pressure levels and SELs exhibited non-monotonic (oscillatory) behavior with range, with up to a 10 dB increase at longer distances.
• Acoustic levels at the shallowest hydrophone exceeded those at deeper hydrophones by 3-10 dB beyond 20 km, indicating surface ducting effects.
• Range-independent bathymetry resulted in approximately 4 dB higher received acoustic levels compared to range-dependent conditions.

Conclusions:

• Long-range acoustic propagation from seismic arrays is complex and influenced by environmental factors.
• The experimental data provides a valuable dataset for validating acoustic source and propagation models.
• Accurate modeling is essential for predicting sound pressure and SEL in the far-field of seismic sources.