Displaying bioacoustic directional information from sonobuoys using "azigrams"

Area of Science:

• Acoustics
• Signal Processing
• Oceanography

Background:

• Directional Frequency Analysis and Recording (DIFAR) sonobuoys provide acoustic particle velocity and pressure.
• Conventional beamforming for azimuth estimation is imprecise and susceptible to noise.
• Accurate source localization is critical for underwater acoustic monitoring.

Purpose of the Study:

• To introduce and demonstrate an alternative multiplicative processing scheme for DIFAR sonobuoys.
• To present the "azigram" as a novel visualization tool for acoustic directionality.
• To show the benefits of azigrams for signal detection and bearing estimation.

Main Methods:

• Multiplicative processing of DIFAR sonobuoy data to compute "active intensity".
• Generation of "azigrams" displaying acoustic azimuth as a function of time and frequency.
• Demonstration using data from multiple locations without signal demultiplexing.

Main Results:

• The azigram method effectively computes dominant noise field directionality.
• Azigrams provide a clear, color-coded display of acoustic azimuth.
• The technique was successfully applied to diagnose sonobuoy issues and improve low signal-to-noise ratio detection.

Conclusions:

• Azigrams offer a computationally efficient and robust alternative to conventional beamforming for DIFAR sonobuoys.
• This method enhances the detectability and bearing estimation of acoustic sources, especially in directional noise.
• Azigrams hold potential for improving signal classification in complex underwater acoustic environments.