Research on the post/starboard discrimination algorithm for twin-line array and the influence of array shape distortion

For surface ships, the towed hydrophones array is usually used to detect azimuth and to track moving targets because of its large aperture. The effective scope of a common sound pressure single array is only 180°, so that the common array cannot determine whether a target is to the left or to the right. While a twin-line array has similarity with a planar array in theory, a twin-line array does have the ability to discriminate between port/starboard. In order for the twin-line array to make post/starboard discrimination, a time delayed addition method and time delayed subtraction method are widely applied in direction finding field. Time-delay addition method obtains bearing time results by adding beam forming outputs, while its post/starboard suppression ratio is small. Time-delay subtraction method, obtains bearing time results by subtracting beam forming outputs. Its post/starboard discrimination ability will decline sharply under the condition of low SNR or where shape distortion of the array existing. Based on the above two algorithms, further research which subtracts bearing time results could obtain new bearing time results and improve post/starboard discrimination ability in low SNR conditions. Furthermore, the shape distortion effect on the performance of this algorithm is also studied in this paper. This paper mainly studied three kinds of influences of shape distortion on post/starboard discrimination ability of the algorithm: twin-line parallel displacement distortion, nonparallel displacement distortion; and, circular arc shape distortion. The experimental simulation results show that shape distortion does influence post/starboard discrimination ability seriously, while the discrimination ability can be recovered well after modification. Therefore, it is necessary to study shape distortion measurement methods and adaptive shape distortion modification algorithms.