Measurements of mid-frequency bottom backscattering strengths on the Outer Hebrides Platform and the Stanton Banks

Abstract

In July 2002, direct-path, mid-frequency (2–5 kHz) bottom backscattering strength measurements were conducted at 21 sites on the Outer Hebrides Platform and the Stanton Banks (northwest of Scotland) during The Technical Cooperation Program’s T-MAST 02 sea trial. This is a complex area, with bottom grabs indicating the wide presence of stones, pebbles, gravel and rocks throughout most of the region. When stones, etc. were present, bottom backscattering strengths were generally high and flattish in angle (over 10 to 40 deg), with many sites empirically exhibiting a sinθ or flatter angular dependence. The frequency dependence in these cases was mild. When stones, etc. were absent, bottom backscattering strengths were less high and less flat in angle, with strong frequency dependence. These results dramatically illustrate the inadequacies of using Lambert’s Law to model bottom backscattering strengths and suggest that active sonars operating in this environment will encounter strong reverberation. [Work supported by ONR.]