Phased subarray processing for underwater 3D acoustic imaging

Absrraef-3D sonar imaging using a fully-populated rectangu-lar ZD array has many promising applications for underwater iniaging. h primary limitation of such systems is the large inuniber of parallel front-end hardware channels needed to process the signals in transmit and receive when using conren-tional full phased array imaging. A subaperture beam acquisi-tion and image formation process is presented that significantly reduces the number of front-end hardware channels while achieving image quality approaching that of full phased array imaging. Rather than transmitting and rerei\,ing on all NXN transducer clemcuts lo form each beam, an MwM subset of ele-ments-alled a subarray-is used for each tiring. The limited number of frost-end processing channels are used to acqnire data from each subarray. Switching hardware allorvs the subar-ray to be nlulliplexed across the full array. Due to the Nyquist sampling criteria in beamspace, the nuniber of beams acquired by each subarray can be significantly reduced compared io the number required for the full array. 'The phased subarray proc-essing includes beam upsampling, lateral interpolation with a subarraydependent filter, and coherent weighting and sumnla-tion of all subarray images to form a high resolution image. The phased array method achieves an image qualit? nearing that of full phased array imaging with significantly fewer processing channels, slightly reduced SNR, and roughly three times the number of firings for reasonable configurations. 1