Waveguide invariant focusing for broadband beamforming in an oceanic waveguide

Area of Science:

• Acoustics
• Signal Processing
• Oceanography

Background:

• Shallow-water environments cause multipath propagation, degrading broadband sonar array processing performance.
• Angularly spread interference, especially near endfire for towed arrays, masks weaker sources of interest.
• Conventional adaptive beamforming requires long observation times for narrowband covariance matrix estimation.

Purpose of the Study:

• To extend wideband focusing techniques to address coherent multipath interference in sonar array processing.
• To develop a method that reduces the observation time needed for covariance matrix estimation.
• To improve array gain and source detection capabilities in challenging shallow-water conditions.

Main Methods:

• Introduced waveguide invariant focusing (WIF) to exploit frequency-dependent horizontal wavenumber differences.
• Developed a method to form wideband covariance matrices without interference rank inflation.
• Simulated WIF performance in a realistic shallow-water ocean environment.

Main Results:

• WIF effectively suppresses coherent multipath interference by treating it as a rank-one subspace across frequencies.
• The proposed method allows for the formation of wideband covariance matrices with reduced observation times.
• Adaptive beamforming using WIF demonstrated significant array gain improvement over conventional methods.

Conclusions:

• Waveguide invariant focusing (WIF) offers a robust solution for adaptive beamforming in shallow-water sonar.
• WIF enables significant performance gains in array processing, particularly for detecting weak sources under multipath conditions.
• The method provides a practical approach for improving sonar system effectiveness with limited data acquisition time.