Suitability of Correlation Arrays and Superresolution for Minehunting ...

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Published by DSTO Systems Sciences Laboratory PO Box 1500 Edinburgh South Australia 5111 Australia Telephone: (08) 8259 5555 Fax: (08) 8259 6567 © Commonwealth of Australia 2002 AR-012-410 July 2002 APPROVED FOR PUBLIC RELEASE
Suitability of Correlation Arrays and Superresolution for Minehunting Sonar Executive Summary As part of the Navy’s minehunting program, the need has been identified to acquire, if possible, improved hull-mounted sonars. These might, in particular, survey an area faster, and/or enable the detection and classification of suspected mines to occur at a greater range. Towards developing such a sonar, a project called ‘Minefinder’ has been set up. As part of Minefinder, work, reported here, has been carried out in two areas. The first area concerns arrays—to be called 'correlation arrays'—that are based on the principle used by correlation telescopes in radio astronomy. The best-known of these devices is the cross-shaped array, constructed from two arms and commonly called the Mills cross. In some sense, such an array of M + N elements performs as well as a conventional array of MN elements. Thus the application of the principle might enable a large reduction in the number of sonar array elements. In this area, key results from the literature are reported and some concepts are elucidated with the aid of mathematics. Key problems are identified: in particular, two problems described in the last paragraph of this summary. The second area is that of superresolution (SR), consisting of methods by which resolution is obtained that is better than that given by the Rayleigh criterion. (The latter states that angular resolution is approximately equal to (wavelength)/(dimension of array).) Potentially SR would produce better sonar images at any given range. In this second area, a more complete literature survey is carried out. A number of SR techniques are briefly described, including Capon's method and an autoregressive moving average (ARMA) model. In SR, while each method has had successes, general conclusions as to the goodness of the methods are in general lacking in the literature. A book by Steinberg and Subbaram is of particular interest, since it, like the Minefinder sonar, is concerned with active imaging. An important problem for the application of the above techniques to sonar is that both SR and correlation arrays apparently require a high signal-to-noise ratio. For both SR and correlation arrays, the application to sonar faces a further key problem. The problem is that correlations usually exist between the return signals from different targets; that is, these signals bear a certain resemblance to each other. These correlations cause the image quality to become degraded. Success therefore requires some method for ‘decorrelating’ the targets. Methods that achieve this under certain circumstances are described.
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Page 32 and 33: DSTO-TN-0443 MUSIC (Section 9.3), S
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Page 38 and 39: DSTO-TN-0443 The above work by SBF
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DISTRIBUTION LIST Suitability of Co
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