Seabed classification using surface backscattering strength versus acoustic frequency and incidence angle measured with vertical, split-beam echosounders

The multifrequency biplanar interferometric imaging technique(MBI) is applied to data from vertical, split-beam echosounders to produce sub-beam estimates of seabed surface-backscattering strength (S-s), incidence angle (theta), and roughness (R). Asimple model is used to quantify the variation of S-s versus theta = {2-20 degrees} and acoustic frequency, f = {18, 38, 70, 120 and 200 kHz}. The coefficients of the angle- and frequency-dependent terms of the model indicate seabed material properties, principally small- and large-scale roughness and hardness. These indices are combined with the estimates of theta and R to classify the seabed using unsupervised cluster analysis. This technique is applied to data from the Forty-Three-Fathom Bank, a seamount in the Southern California Bight. The resulting seabed classifications are consistent with the surficial lithology and the spatial distribution of known rockfish (Sebastes spp.) habitat. The method should be generally applicable to seabed classification.