A noncoherent correlation technique and focused beamforming for ultrasonic underwater imaging: a comparative analysis

The purpose of this paper is to describe a noncoherent correlation technique for the formation of 3-D acoustic images, mainly for underwater applications. This technique is applied to the envelope of signals received by a 2-D array. The performances of the technique are compared with those of the coherent technique of focused beamforming in terms of angular resolution, depth of field, beam pattern, and accuracy in range determination. Moreover, special attention is given to the modalities for an efficient implementation on a digital computer. The complete absence of grating lobes, for whatever arrangement of the transducers, and the much higher speed of the imaging process, as compared with that of beamforming in the time domain, are the two major advantages of this technique. A reduction in the speckle effect, the possibility of creating a virtual depth of field, the feasibility of using square-law transducers, and the implementation simplicity are additional interesting characteristics. The results of some simulations are reported and compared with those obtained by the beamforming process.<>