ABSTRACT: Using Side-Scan Sonar to Look at Buried Surfaces

Quentin J. Huggett, Alan K. Cooper

GLORIA side-scan sonar images commonly show a distinct pattern of acoustic artifacts that have been identified as interference fringes. These fringes are caused by thin-layer interference that occurs when some of the sound reaching the sea floor penetrates it and is reflected off a buried surface. Sound backscattered at the sea floor interferes constructively or destructively with sound reflected from the subsurface, depending upon the difference in length between the two sound paths. Thus, as range from the ship increases, the path difference decreases; so sound moves in and out of phase, causing bands of greater and lesser intensity on the GLORIA sonograph. Variations in the fringe pattern on the GLORIA sonographs relate to changes in the depth of the buried surface. Fr nges and bathymetric data from adjacent ships' tracks can provide insight into the shallow three-dimensional structure of sediment bodies down to a maximum depth of about 5 m.

The most persistent occurrence of fringes was observed in the deep Bering Sea. Here, their persistence enabled them to be recognized and their basic geometry described. Elsewhere, interference fringes are usually found in association with deep ocean channel/fan systems or on poorly consolidated sediments. Areas adjacent to the Surveyor Channel and Chile Trench are classic examples of this.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990