Ultrawideband Underwater Real-Time 3-D Acoustical Imaging With Ultrasparse Arrays

Large 2-D arrays are indispensable for underwater high-resolution real-time 3-D acoustical imaging, which however must be thinned significantly to avoid an overly high cost. The existing methods have decreased the number of elements from tens of thousands to several hundreds, which is still excessive for the implementation of underwater 3-D acoustical imaging system. Reported to be able to achieve an ultralow hardware cost in other fields, the ultrawideband (UWB) technology is introduced in this paper for the purpose of underwater real-time 3-D acoustical imaging. First, this paper reveals that the UWB technology is feasible for underwater 3-D acoustical imaging. Second, by analyzing the beam-steering properties of UWB underwater 2-D arrays, this paper demonstrates that although tens of elements are enough to achieve the required resolution and sidelobe level, they cannot guarantee the signal-to-noise ratio (SNR) for high imaging quality. Third, this paper proposes to employ the modulated excitation technique to increase the SNR in the underwater application. The analysis of computational load indicates that the modulated excitation technique has few influences on the implementation of underwater real-time 3-D acoustical imaging systems. At last, this paper presents a prototype of UWB underwater real-time 3-D acoustical imaging system with a 32-elements annular array, of which the performance is evaluated to verify the advantages of applying the UWB technology to underwater real-time 3-D acoustical imaging.