In this animation, the bottom surface is represented by a white wire-mesh screen, through which the sub-bottom sediments can be seen. Each stack of ``tennis'' balls represents the acoustic echo of a single dual-frequency signal.

Ball colors represent sediment type as classified according to wet density as measured by acoustic impedance, and range from red, for the softest fluid mud, through yellow for intermediate density silty clays, to green for densest material like sand, gravel, and rock. Successive balls are about half a foot apart in each stack. Locations of surface density measurements, most made with the Army Corps fathmometer, are shown as x's whose colors represent the sediment type indicated by this instrument.

It is very unusual for a stack to indicate high density sediments on top of less dense material.

Small hills and bumps on the bottom, like those near Brashear Island close to the end of the animation, are comprised of and underlain by mostly harder material, while stacks in low spots and depressions are usually capped by red balls, indicating a layer of softer, less dense material.

Notice how quickly your eye tries to construct horizontal connections among stacks to establish horizontal transitions between sediment types.

We are extending our interpolation and visualization efforts into the third dimension in order to investigate the shape and position of the horizontal transition planes between each of these sediment types. Because the softer sediments have the greatest potential for sorption of contaminants, their location is important. Moreover, a 3D interpolation will allow estimation of the volume of potentially contaminated sediment, as well as the volume of overburden which covers it. These estimates are important considerations for evaluation of possible remediation and selection of remediation techniques.