Seabed and sub-bottom classification using measurements of normal incidence backscatter from 1–10 kHz

Abstract

It has been established that the first and second normal incidence acoustic returned from the seabed can be used as a classification tool to discriminate between different sediments. Typically this is accomplished using monostatic echosounder systems that operate in the range of several 10 s of kHz so that bottom roughness at the seabed interface is the dominant scattering mechanism. Model results (Hines and Heald, Proceedings of the Institute of Acoustics Conference on Acoustical Oceanography, Southampton, UK, April 2001) indicate that at lower frequencies, normal incidence returns from the sub-bottom should provide an additional discrimination tool without significantly corrupting the information contained in the interface scatter returns. This paper presents an experimental methodology for making these measurements in the 1 to 10 kHz frequency band using a vertical line array of receivers and a downward-looking superdirective projector array. Results from experiments at the ONR Strataform area and Scotian Shelf will be compared with independent geo-acoustic information.