A Technique to Assess the Characteristics of Bottom and Subbottom Marine Sediments.

Abstract : This report presents the theoretical concept, assembly, and field testing of a waterborne seismic acoustic impedance technique which has been developed to characterize bottom and subbottom sediments as they relate to removal by dredging. This method, developed under the Dredging Research Program (DRP), provides estimates of in situ density and soil type in a rapid, cost effective manner using digital acoustic subbottom profiling methodology. In situ densities obtained by the acoustic impedance technique to date, when compared to those obtained by conventional means at several different sites under a wide variety of marine conditions, have statistically been with jlO percent. However, only marine sediments considered to be fully saturated, inorganic, and uncontaminated have been investigated and "ground truthed." After comparisons with ground truth information and laboratory testing, a critical analysis of the acoustic impedance technique reveals it to be a valid and useful approach to bottom and subbottom material and density prediction. While some development is still needed to fully establish advantages and limitations, its potential usefulness warrants technology transfer now, provided proper cautions are observed.