Single beam echosounding: Considerations of depth and seabed slope

Abstract

The topic of depth compensation of single beam echo time series for seabed classification is fairly well studied. The effect of seabed slope has not been publicized. In applications for seabed classification, seabed slope is observed to be associated with classification inaccuracy and failure. In cases of higher slope, single beam bathymetry also becomes inaccurate. A survey of 2 fjords with extreme variation in slope is presented as a representative example and testing bed for investigating slope. The direct effect on seabed echoes is investigated and explained in reference to a simple model of beam-echo geometry. Survey bathymetry is compensated for slope; inaccuracies of up to 5% of depth are corrected, however bottom picking accuracy is diminished in areas of slope and cannot be improved. Surveys of a gas hydrate site and a river will also be presented as applications of these ideas. Early results from BORIS model studies of methods for compensation of slope and depth may also be presented.

What can a low-cost fish-finder tell us about the seabed?

“…Because of the spherical symmetry of the sound wave emitted by the transducer and the attenuation through the water column, the echo intensity depends on the distance travelled and must be corrected to remove depth effects (Biffard et al, 2005(Biffard et al, , 2010Caughey & Kirlin, 1996;Pouliquen, 2004;Rodríguez-Pérez et al, 2014) (see Fig. 3).…”