High-resolution sonar imaging using sparse transmitting and dense receiving arrays

An imaging sonar usually uses a large aperture hydrophone array to obtain a fine angle resolution, leading to a high system cost. To obtain a high angle resolution with a limited number of elements, we propose a new imaging method which uses a sparse M-element transmitting uniform linear array (ULA) and a dense N-element receiving ULA. The inter-element spacing of the transmitting ULA (i.e., dt) and that of the receiving ULA (i.e., dr) satisfy dt=Ndr. The sparse transmitting ULA produces multiple grating lobes to discretely illuminate the target scene, and the receiving beams (produced by the dense ULA) are steered to these grating lobes. Thus, in a ping the scanning beam number is equal to that of grating lobes. Meanwhile, the multi-ping illumination is utilized to produce enough grating lobes (by changing the transmitting mainlobe direction for different pings) to cover the target scene. Moreover, the array manifold errors of the transmitting and receiving ULAs are also taken into consideration, and the relative influences on the beampattern and the imaging result are analyzed. Numerical simulation show that the proposed method has a similar imaging ability to the MNelement ULA by using only (M+N) physical elements.