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access icon free Appendix 4: An example of masquerading

A specific example will now be given, in which two distinct two-mode toy problems, A and B, give almost identical signals in the eight-loop vertical array. Data are shown for three frames, but the method of deriving the ray parameters for B from those for A is so general that the masquerading can in fact continue indefinitely. The frequency is 6 MHz. Continued manipulation of equations of this kind leads to the conviction that any two-mode problem involving angles below 15-2° (at least) at 6 MHz can be masqueraded by some other problem involving two or more modes. One mode can masquerade as two, but in this case the amplitude fluctuations of the two modes would show a strong correlation. Masquerading occurs chiefly at low frequencies and low-elevation angles and is a manifestation of inadequate resolving power. On this physical interpretation, it cannot be avoided by alterations in the number and dispositions of the elements within a given aperture; it can arise with irregular, as well as regular, spacings.

Inspec keywords: correlation methods; array signal processing

Other keywords: eight-loop vertical array; ray parameter; frequency 6 MHz; correlation; low-elevation angle; two-mode toy problem; identical signal; masquerading

Subjects: Signal processing and detection

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