LAUSR

Acoustical imaging systems are an important kind of instrumentation for underwater investigation. Currently, angular resolutions of most existing real-time underwater 3-D imaging systems are around 1°, which cannot meet the high-quality imaging requirement in a relatively far distance. Enhancing the angular resolution of a real-time 3-D imaging system needs enlarging the aperture size of its receiving 2-D array. However, the huge number of elements is not affordable for a traditional fully sampled uniform large 2-D array with half-wavelength interelement spacing to achieve a high angular resolution. This paper proposes the concept of ultralarge ultrasparse ultra-wideband (UUU) 2-D arrays for achieving the high angular resolution of underwater 3-D acoustical imaging systems. The design method of UUU 2-D arrays is demonstrated through the example of designing an annular 2-D array with only 100 elements. The capabilities of the designed annular UUU 2-D array are evaluated, showing that it can achieve a 0.1° angular resolution and a −32 dB maximum sidelobe level. The imaging simulations of complicated targets also demonstrate that the designed annular UUU 2-D array can satisfy the requirement of high-resolution underwater 3-D acoustical imaging. The element number of the designed annular UUU 2-D array is 4 orders of magnitude lower than that of a fully sampled uniform 2-D array, which provides a viable choice for developing high-resolution real-time underwater 3-D acoustical imaging systems.