Spatially variant autofocus for circular synthetic aperture sonar

Area of Science:

• Underwater acoustics
• Sonar imaging
• Signal processing

Background:

• Circular synthetic aperture sonar (CSAS) offers enhanced resolution and target detection.
• CSAS data autofocusing is challenging due to large apertures and elevation sensitivity.
• Existing autofocusing methods often lack practicality.

Purpose of the Study:

• To extend the multilateration autofocusing technique for circular synthetic aperture sonar (CSAS).
• To simultaneously solve navigation and elevation estimation problems in CSAS focusing.
• To improve the stability and robustness of CSAS autofocusing.

Main Methods:

• Extension of map-drift based multipoint autofocus (multilateration) for CSAS.
• Joint estimation of navigation solution and coordinate corrections for control patches.
• Development of methods for inverse problem stability and adaptive weighting for outlier reduction.

Main Results:

• Demonstrated near-optimal point-spread functions on natural isotropic scatterers.
• Achieved robust performance in areas with bathymetric variability.
• Successfully addressed aberration spatial variance with 3D navigation correction.

Conclusions:

• The extended multilateration approach provides a practical and effective solution for CSAS autofocusing.
• The method significantly improves image quality and system robustness.
• This technique advances the capabilities of sonar imaging for underwater applications.