Ground roll waves traveling across the seabed provide extra information, their direction of rotation, compared with plane waves in fluids or solids. Idealized Rayleigh waves are "retrograde" in that their horizontal particle motion opposes the direction of travel of the wave when the interface is raised. A single point measurement near the seabed can determine this rotation. In water, there are associated evanescent pressure waves that are largely confined to the bottom, likely to affect fish and other creatures near the seabed during pile driving. The directional information may prove key to the lifestyle of such creatures.
Keywords: Ambiguity; Directionality; Evanescent; Piling noise.