Enhanced underwater three-dimensional imaging using acoustic orbital angular momentum waves and mode matching beamforming

Improving the underwater three-dimensional imaging resolution of a sonar system is of great significance to achieving high-precision ocean exploration results. Actually, improving the resolution can be considered from the perspective of information acquisition. The acoustic orbital angular momentum (AOAM) wave has a modal dimension and can carry more target information. However, there are few studies on the application of AOAM waves for underwater three-dimensional imaging. This paper establishes the related signal models of the AOAM wave in underwater imaging and examines the sound field characteristics from both simulation and underwater real test data. A method called mode matching beamforming (MMBF) is proposed, and a composite structure of uniform circular array (UCA) plus spiral array is combined to study the imaging performance of AOAM waves and plane waves. The simulation results indicate that, compared with the plane wave, the sidelobe in the AOAM wave imaging beam pattern reaches -22.43 and -29.10 dB in the azimuth and elevation angles, respectively, and the mainlobe widths are reduced by 1.70° and 0.40° in both directions. Finally, this paper uses the MMBF method to process the echo data of underwater real object and realizes the imaging of the corner reflector.