Deep water towed array measurements at close range.

Area of Science:

• Oceanography
• Acoustics
• Geophysics

Background:

• Towed array receptions were collected during the North Pacific Acoustic Laboratory Philippine Sea 2009 experiment.
• Acoustic signals were transmitted using narrowband tones and broadband pulses across the 79-535 Hz frequency band.
• Received acoustic energy primarily followed direct and bottom bounce paths.

Purpose of the Study:

• To investigate the spread in acoustic arrivals, particularly bottom bounce energy.
• To model acoustic propagation using measured environmental data.
• To differentiate between in-plane and out-of-plane scattering effects.

Main Methods:

• Collected towed array receptions from a towed source during ship transits.
• Utilized narrowband tones and broadband pulses for acoustic transmissions.
• Performed two-dimensional acoustic propagation modeling with bathymetry, geoacoustic parameters, and sound-speed fields.
• Incorporated seafloor roughness and surface wave effects into the models.

Main Results:

• Bearing-time records showed a 35° spread in bottom bounce arrival angles.
• Doppler processing revealed significant frequency spread in bottom bounce energy.
• In-plane scattering from rough interfaces explained much of the observed arrival spread.
• Out-of-plane scattering was observed at short ranges and not fully explained by in-plane roughness modeling.

Conclusions:

• Seafloor roughness and surface waves are significant factors in acoustic propagation modeling.
• In-plane scattering adequately explains some, but not all, observed acoustic phenomena.
• Out-of-plane scattering, particularly at short ranges, requires further analysis and may indicate complex scattering mechanisms.