A Computer-Based Electro-Optical System for Measuring Wave-Induced Sand Concentrations

A computer-based system utilizing an electro-optical instrument has been developed for generating and processing a signal proportional to the instantaneous sand concentration at a point in a flow field. Herein are described the instrumentation and techniques used in a study of sediment entrainment by periodic waves breaking on sand beaches. The instantaneous sediment concentration has been decomposed as follows: where C(x, y, z) is the temporal average concentration, C^′(x, y, z, t) is a random component of the sediment concentration, and C_p(x, y, z, t) is a repetitive component with period equal to the period of the breaking waves. Particular attention has been given to isolating the repetitive component which was so obscured by the signal characteristics that no periodicity was apparent on either an oscilloscope trace or a strip chart recorder. Spectral analysis was not applicable because the shape of the repetitive waveform, C_p(x, y, z, t), over one wave cycle was desired.