A high speed multi-channel data acquisition system for remote acoustic sediment transport studies

Hay, Alex E.; Huang, Li; Colbourne, Eugene; Sheng, Jinyu; Bowen, Anthony

doi:10.1109/oceans.1988.23536

Cited by 5 publications

(4 citation statements)

References 5 publications

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“…There is good agreement in terms of both the maximum amplitude and the duration of sediment suspension events, particularly in the cases with low and intermediate wave energy (Figures 11 and 12), for which the suspension events are clearly associated with wave groups. (The association between groupiness in the wave forcing and sediment suspension has been noted previously [Hay et al, 1988;Greenwood et al, 1990;Hanes, 1991]). There can also be seen in some instances, though not all, a clear association between the variations in at least one of the concentration estimates and the individual wave cycles within a wave group.…”

Section: Therefore the Height Above Bottom Of Obs 133 Hobs Was Detesupporting

confidence: 52%

“…The acoustic backscatter measurements were made with RASTRAN (remote acoustic sediment transport measurement) system 1. A detailed description of the data acquisition and operating characteristics of an early version of this system is given elsewhere [Hay et al, 1988]. Subsequent improvements are outlined by Hay [1991].…”

Section: Laboratory and Field Methodsmentioning

confidence: 99%

“…The total scattering cross section contributes to the attenuation of the incident and backscattered sound waves passing through a cloud of suspended particles. An expression for the total scattering cross section of natural sand grains, based on the relatively old measurements made by Flareruer [1962], is available [Sheng and Hay, 1988]. Measurements of the backscatter cross section have been made by Hay [1991].…”

Section: Introductionmentioning

confidence: 99%

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Vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter

Hay¹,

Sheng²

1992

J. Geophys. Res.

179

109

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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.

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Section: Therefore the Height Above Bottom Of Obs 133 Hobs Was Detesupporting

confidence: 52%

Section: Laboratory and Field Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter

Hay¹,

Sheng²

1992

J. Geophys. Res.

179

109

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“…The data were collected at Stanhope Lane Beach with remote acoustic sediment transport (RASTRAN) system 1 [Hay et al, 1988;Hay, 1991]. Figure 1 shows Figure 2).…”

Section: Experimental Methodsmentioning

confidence: 99%

Spatially correlated depth changes in the nearshore zone during autumn storms

Hay¹,

Bowen²

1993

J. Geophys. Res.

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Acoustic reflection measurements of seabed elevation were made at Stanhope Beach, Prince Edward Island, during three successive storms in October‐November 1989. The instruments were located approximately 200 m offshore on the seaward face of a shore parallel bar in a mean water depth of 2.2 m. Bed elevation measurements were made at 30‐min intervals with a range resolution of ±1 mm at horizontal spacings between 22 cm and 1.5 m, using an array of four acoustic sounders operating at 1, 2.25, and 5 MHz. It is shown that such an array can be used as (1) an interferometer to determine bedform properties and migration rates, (2) a leveling device to determine changes in local bottom slope, and (3) an erosion/deposition gauge. In the interferometric mode, time domain autocorrelation and cross‐correlation analyses of the bottom elevations are used to estimate the wavelengths, migration rates, and migration directions of sand ripples and megaripples. The ripple wavelengths (10–15 cm) and heights (3–5 cm) are comparable to measurements made by divers. Ripple migration rates were 1–6 cm h−1 directed offshore in the direction of the mean shore normal near‐bottom current and increased with increasing mean current speed. Evidence of megaripple‐like features (2–5 cm height; 1.5–3 m length) is found, also migrating in the direction of the mean shore normal near‐bottom drift, at speeds of about 20 cm h−1. Bedload transport rates in the onshore‐offshore direction are estimated from the bedform migration rates. The ripple transport rate was small (an order of magnitude smaller than the transport of sediments in suspension by the mean offshore drift). In contrast, the large‐scale bedform transport appears to have been comparable to the mean current transport of suspended sediment. Interestingly, it appears that the total bedform transport was comparable to that predicted by Watanabe's (1981) net bedload transport formula, provided a coefficient appropriate to irregular wave conditions is used. During the third and highest‐energy storm event, the measurements indicate transition to flat bed, and generalized local erosion at a maximum rate of 8 cm h−1. This erosion event was associated with a general shoreward migration of the bar.

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Nearshore Sediment Flux and Bottom Boundary Dynamics the Canadian Coastal Sediment Transport Programme (C-Coast)

Greenwood

Osborne

Bowen

et al. 1991

Coastal Engineering 1990

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A high speed multi-channel data acquisition system for remote acoustic sediment transport studies

Cited by 5 publications

References 5 publications

Vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter

Vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter

Spatially correlated depth changes in the nearshore zone during autumn storms

Nearshore Sediment Flux and Bottom Boundary Dynamics the Canadian Coastal Sediment Transport Programme (C-Coast)

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