Author(s): L. Zedel; A. E. Hay
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Abstract: Acoustic systems provide great potential for non-invasive sampling of near bottom sediment transport processes: acoustic backscatter can be inverted to infer the concentration of suspended particles, and the Doppler shift can be used to determine flow speeds. We present a coherent Doppler system employing multiple frequencies between 1.2 and 2.4 MHz. The use of multiple frequencies allows ambiguity resolution in the coherent Doppler velocity and can also be used for the estimation of suspended particle size distribution. The combination of measurements allows direct estimation of the sediment transport flux. As with any acoustic system design there are many performance characteristics that must be taken into consideration and the use of multiple frequencies further complicates this problem. The design process was facilitated through use of a model of coherent acoustic backscatter developed for this purpose. We present the principles of coherent sonar systems in general. The prototype system can generate three component velocity profiles with 0.3 cm range resolution over a 40 cm range at a rate of up to 100 per second. Horizontal velocities as high as 4 m s-1can be resolved. System performance is demonstrated with model simulations and examples from laboratory observations.
Year: 2009