"Proceedings, Federal Interagency Workshop,
"Sediment Technology for the 21'st Century,"
St. Petersburg, FL, February 17-19, 1998"

Development of an Suspended Sediment Measurement System (SSMS)

By Robert Derrow II

Pre-Proposal

Issue/Problem

Use of acoustic techniques to measure suspended sediment concentration have been ongoing for several years (Urick, 1948). In most of these systems a short burst of high frequency (>1 MHz) sound is emitted from a transducer(s) and is scattered off the sediment in suspension. The magnitude of the backscattered energy is related to the concentration and size of the sediment. Current technology can measure suspended sediment concentration with limited size distributions with high accuracy (Schat, 1997), but success has been limited at determining sediment size distribution to a reasonable accuracy. Very high concentrations where multiple scattering effects are more dominant are especially problematic (Crawford and Hay, 1993; Thorne et al., 1994). We propose to develop a system to minimize the current limitations mentioned above.

Beneficiaries

This instrument would be useful to all organizations that are involved with, or concerned about, knowing what the size and concentration of sediment transported in suspension whether in a stream, river, estuary, or marine environment.

Objectives

To develop a lab/field useable system that will remotely monitor suspended sediment concentration and size distribution in various measurement areas.

Approach

A system will be built from custom and COTS components that utilize 3 or more acoustic transducers that operate at different frequencies. The backscatter from the individual transducers will be analyzed individually and in pairs to build up sediment size/backscatter ratio curves that produce average concentration/size information about the sediment profiles. To start with, the system will be calibrated using the existing Suspended Sediment Calibration Tower. Then laboratory flume measurements will be conducted followed by field tests at an instrumented flume in the Goodwin Creek Watershed.

Funding

Funding by Fiscal Year:
FY98$100K
FY99 $100K
FY00 $100K

Principal Investigator

Rob Derrow & Roger Kuhnle

References

Crawford, A.M. and Hay, A.E., 1993, Determining suspended sand size and concentration from multifrequency acoustic backscatter, J. Acoust. Soc. Am., 94 (6), 3312-3324.

Schat, J., 1997, Multifrequency acoustic measurement of concentration and grain size of suspended sand in water, J. Acoust. Soc. Am., 101 (1), 209-217.

Thorne, P.D., Hardcastle, P.J., Flatt, D, and Humphery, J.D., 1994, On the Use of Acoustics for Measuring Shallow Water Suspended Sediment Processes, IEEE J. Oceanic Engineering, 19 (1), 48-57.

Urick, R.J. 1948, The absorption of sound in suspensions of irregular particles, J. Acoust. Soc. Am., 20, 283-289.


upWorkshop Contributions


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