Synchronous 3-D Imaging and Velocity Estimation of Underwater Targets Using Pulse-Pair Acoustical Imaging Technique

Abstract

Velocity, position, and geometry are key parameters for sonar applications in underwater target detection, classification, and tracking. Current underwater 3-D acoustical imaging techniques can provide much more geometric details of the underwater targets by high-resolution acoustic images. However, they cannot conduct target velocity estimations simultaneously. Kinematic information (i.e., Doppler shifts) of the targets has been lost during imaging since these techniques are essentially developed for obtaining static images. Therefore, this article proposes a “pulse-pair” acoustical imaging (PPAI) technique to acquire geometry, velocity, and distance information of underwater targets simultaneously in a single ping. Instead of transmitting a single pulse to collect echoes from the underwater environment like the conventional acoustical imaging techniques, a “pulse-pair” transmission scheme is proposed to realize 3-D underwater imaging in the PPAI method. The radial velocities of underwater targets are estimated in all target-existing volumetric cells by a pulse-pair autocorrelation method. Considering that a pulse-pair transmission should cause duplication and a mixture of the original image (image blurring), a deconvolution algorithm is adopted to correct the mixed image. The performance of the proposed method is evaluated with a high-resolution 3-D PPAI prototype in a simulation underwater 3-D scenario. Simulation results show that 3-D geometry and velocity features, as well as distances of underwater targets, can be effectively acquired in a single ping with the proposed method. It is significant for sonar applications to avoid possible changes in target features over time due to the relatively long propagation time of sound.