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Interference fringes on GLORIA side-scan sonar images from the Bering sea and their implications
Huggett, Q.J.; Cooper, A.K.; Somers, M.L.; Stubbs, A.R. (1992). Interference fringes on GLORIA side-scan sonar images from the Bering sea and their implications. Mar. Geophys. Res. 14(1): 47-63
In: Marine Geophysical Researches. Reidel: Dordrecht. ISSN 0025-3235, more
Peer reviewed article  

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Keywords
    Gloria; Interferometry; Ocean floor; Scattering layers; Sediment structure; Side scan sonar; Sound scattering; Marine

Authors  Top 
  • Huggett, Q.J.
  • Cooper, A.K.
  • Somers, M.L.
  • Stubbs, A.R.

Abstract
    GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea.

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