Abstract
Vertical profiles of suspended sand concentration and size are obtained from multifrequency acoustic profiling data collected in 1989 during a nearshore experiment at Stanhope Lane Beach, Prince Edward Island. The data were acquired with acoustic sounders operating at 1, 2.25, and 5 MHz. Independent estimates of concentration were made using optical backscatter sensors (OBSs). The algorithm for inversion of the three‐frequency backscatter data to particle size and concentration, based on the ratios of the different signals, was tested in laboratory experiments with an unconfined high Reynolds number suspended sediment jet. Results from the Stanhope Beach experiment are presented for three different surface wave energy regimes, with significant wave orbital velocities ranging from 0.3 to 0.8 m/s and peak wave periods of 4–6 s. The acoustic estimates of mean concentration are shown to be within 10% on average of those determined with the OBS nearest the bottom at 5‐ to 10‐cm height, over time scales ranging from 6.5 min to 4–6 s (one wave period). The acoustic estimates of suspended sediment size near the bottom are within 5–20% of the bottom sediment mean size. The statistical variability of the size estimates is high, with standard deviations in the estimates ranging between 30 and 50% of the mean. The time‐averaged concentration profiles exhibit an exponential decrease with height above an O(10)‐cm‐thick near‐bottom region of nonexpo‐nential decrease. In contrast, the time‐averaged mean size profiles decrease approximately linearly with height, and rather slowly, about 25% in 0.5 m.
Published Version
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