Standing Wave Measurements of Bedload Thickness: Feasibility in an Air System with Model Sedimentby Paul R. Ogushwitz, PRO Scientific Consulting, Denville, United States,
Howard L. Ogushwitz, PRO Scientific Consulting, Denville, United States,
Abstract: A novel technique would yield information about bedload thickness from measurements of a standing wave pattern produced by a sound source insonifying the bottom at normal incidence. The demonstration of feasibility consisted of two key elements: (1) the production of a reproducible standing wave pattern in air in an experimental apparatus, and (2) a mathematical demonstration that an analogous interference pattern would be detectable in water-saturated sand. The position of an interference node in the air system was measured with a repeatability of 1 mm. Because of the large acoustical impedance contrast of sand in air, actual sand sediment was not appropriate for the test measurements. We were therefore led to develop a model sediment, whose physical properties are analogous to the properties of water-saturated sand in an underwater environment. A theoretical relationship between the sediment thickness and the phase of the interference pattern was derived, and the theory agrees well with the measurements. In an underwater system, bedload thicknesses of 2.8 mm or smaller may be measurable, depending on how precisely the interference nodes can be located.
Subject Headings: Wave measurement | Thickness | Standing waves | Sediment | Flow measurement | Bed loads | Soil gas
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