Progress in the Application of the Phase Closure Technique to High Resolution Passive Sonar Imaging.

摘要

A significant improvement has been developed in the first few months of this program that allows the phase closure technique to deal more correctly with the case of distributed inhomogeneities. Our modification of the phase closure technique, to which we refer as cross-correlated subarrays involves processing the hydrophone signals in groups, corresponding to operating the array as a series of smaller subarrays. The beamwidth of a subarray is chosen to restrict the response of the system to the angular field over which the assumptions of phase closure are valid. If we let delta x sub c be the coherence scale of the system (a function of oceanic parameters, together with range R and wavelength lambda), then for phase closure to be valid (with or without cross-correlated subarrays) we require delta x sub c less than or equal to (lambda R) to the 1/2 power. Cross-correlated subarrays are required explicitly if the maximum source separation, s, is such that s > delta x sub c. These expectations have been tested by means of a series of numerical experiments. The results are consistant with the predictions, giving us confidence that the main features of our algorithm are correct. The next step is to apply the algorithm to actual sonar patrol data, to be obtained from Autonetics Marine Systems Division of Rockwell International. Pending the outcome of these tests, we expect that the algorithm should provide a practical and effective method for improving the quality of passive sonar image. (Author)