Bottom backscattering strengths measured at 2-5 kHz in shallow water west of Scotland

During The Technical Cooperation Program´s T-MAST 02 sea trial in July of 2002, direct-path measurements of bottom backscattering strength were made at 2-5 kHz at 18 sites on the Outer Hebrides Platform and the Stanton Banks (west of Scotland). This is a complex area, with sediment types including mud, sand, gravel and bedrock, and strewn throughout with stones, pebbles, and rocks. When stones, etc. were present in accompanying bottom grabs, bottom backscattering strengths were generally high and flatfish in angle (over 10 to 40 deg), with many sites empirically exhibiting a sinthetas 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 stronger frequency dependence. These results illustrate the inadequacies of using Lambert´s Law to model bottom backscattering strengths, as well as relying on archival databases, and argue for in-situ environmental characterization