Determining tomographic arrival times based on matched filter processing: considering the impact of ocean waves

Area of Science:

• Ocean acoustics
• Wave propagation
• Signal processing

Background:

• Acoustic tomography relies on accurate travel time estimation.
• The flat-surface specular ray path is often assumed to provide the best estimate.
• Ocean surface waves introduce complexities not fully accounted for in simple models.

Purpose of the Study:

• Investigate the impact of wave-induced multi-path arrivals on acoustic signal travel time estimation.
• Determine if the largest matched filter magnitude reliably indicates the flat-surface specular ray path arrival time.
• Analyze how surface reflections influence signal fidelity in acoustic tomography.

Main Methods:

• Development of a simple reflection model for in-plane, multi-path arrivals.
• Analysis of ray paths striking the ocean surface multiple times.
• Simulation of signal interference due to simultaneous multi-path arrivals.

Main Results:

• The number of multi-path rays increases significantly with multiple surface interactions.
• Multi-path rays often arrive nearly simultaneously, causing constructive and destructive interference.
• A multi-path ray was observed to closely follow the flat-surface specular path in test cases.

Conclusions:

• Multi-path arrivals from ocean surface waves distort received acoustic signals.
• Matched filter maxima are not always reliable indicators of flat-surface specular ray path arrival times.
• The assumption of using the largest matched filter magnitude needs re-evaluation in wave-affected environments.