The 3D Imaging for Underwater Objects Using SAS Processing Based on Sparse Planar Array

Abstract

Acoustic imaging of underwater objects has to include targets of two kinds which are unburied and buried, so that it can demonstrate the underwater environment thoroughly. Especially for the buried objects, it is much more difficult than unburied ones to obtain a qualified acoustical image due to the high backscattering reverberation generated by buried sediments. The three-dimensional downward-looking synthetic aperture sonar(SAS) imaging algorithm based on T-type sparse planar array is presented here to quantify and enhance the performance of underwater objects imaging and to improve the efficiency of sonar mapping as well. Pulse compression, multi narrow-beam nearfield beamforming and synthetic aperture method are applied in vertical direction, across-track direction and along-track direction, respectively. The simulation results show that with regard to the along-track direction, resolution is dependent on the length of the physical aperture and central frequency, as well as irrelevant to the range. Meanwhile, the signal-to-noise ratio(SNR) of image improves with the increase of the length of the synthetic aperture. The across-track direction resolution, however, degrades with the increase of the number of the along-track array elements. Moreover, the method is applied to the sea-trial data of shallow seawater area, where the depth of water is approximately 100 meters and the linear objects are buried at depth of about 3 meters. The results show that the presented algorithm is capable of leading the qualified imaging results for underwater targets.