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Single Frequency Acoustics

Single frequency acoustics is a method to estimate suspended sediment.

This method can be used if sand content is of interest and the river depth and width is adequate to profile in multiple “bins”, but there is not a large range in sand grain size, or a large ratio in the ratio of fines (silt and clay) to sand. An acoustic Doppler velocity meter (ADVM) deployed in a fixed location, usually as part of a streamgage, horizontally profiles (sidelooking) acoustic backscatter data within a known volume of water.

Cross-sectional illustration of the river channel looking downstream showing different acoustic instruments.

These backscatter data are processed and corrected for variables affecting the backscatter signal such as water absorption and sediment attenuation. Suspended-sediment concentrations (SSCs) from discrete, isokinetic, depth-integrated suspended-sediment samples are then related to the corrected backscatter signal to develop a sediment-acoustic rating.  

Illustration cross-sectional view of a river showing different acoustic instruments.
Image of a person by a river near a bridge with an acoustic Doppler velocity meter (ADVM)

 

Beam Calibration: The Federal Interagency Sedimentation Project (FISP) has funded an effort to establish an ADVM beam calibration procedure against a known sound source at the USGS Hydrologic Instrumentation Facility (HIF). The goal of this procedure is to allow users of the sidelooking sediment-acoustic index methods to exchange ADVMs of the same make and model by having a correction method associated with the ADVM that can be applied to the backscatter record. This would make it possible to compare sediment records from different ADVMs and would not require the development of a new rating if one ADVM is destroyed or malfunctions. If an ADVM that has been calibrated needs to be sent in for repair, a backup ADVM can be temporarily installed at the site to prevent missing record. 

 

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