Investigation into the application of cross-correlation analysis on acoustic backscattered signals from suspended sediments to measure nearbed current profiles |
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| Institution: | 11. Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead, Merseyside L43 7RA, UK;1. Rotman Research Institute, Baycrest Academy for Research and Education, M6A 2E1 North York, ON, Canada;2. Department of Psychology, University of Toronto, M5S 1A1 Toronto, ON, Canada;1. Department of Chemistry, Indian Institute of Space Science and Technology, Thiruvananthapuram, 695 547, India;2. Vikram Sarabhai Space Centre, Thiruvananthapuram, 695 022, India;1. Department of Remote Sensing and Photogrammetry, Finnish Geospatial Research Institute FGI, Geodeetinrinne 2, FI-02430 Masala, Finland;2. Department of Cartography, São Paulo State University UNESP, Rua Roberto Simonsen 305, 19060-900 Presidente Prudente, Brazil;1. Department of Educational Science, University of Freiburg, Germany;2. Leibniz-Institut für Wissensmedien, Tübingen, Germany;3. Department of Psychology, University of Tübingen, Germany |
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| Abstract: | In the present work, the potential of correlation methods applied to acoustic signals backscattered from suspended sediments, is examined with regard to the measurement of near-bed vertical profiles of the horizontal current velocity. The technique uses the cross-correlation of the backscattered signal between pairs of downward looking horizontally separated transducers, to measure the time taken for suspension structures to advect from one transducer to another. This approach requires a degree of spatial coherence in the suspension field, and advantage is taken of this coherence to measure the flow. To investigate the technique, backscattered data collected using an array of transducers has been examined. The array was deployed along stream in an estuarine environment, which was subject to strong rectilinear currents, and high levels of suspended sediment concentration. Using pairs of transducers with separations between 0.25–5.42 m, the structure of the suspension field has been assessed, the implication of these observations for measuring flow discussed, and nearbed measurements of current profiles obtained. The results show that in the estuarine environment investigated, if the transducer pair separation was of the order of a metre or less, and currents were sufficient to retain sediments in suspension, vertical profiles of the horizontal current could be measured. To assess the results conventional electromagnetic and impeller current meter measurements were collected at four heights above the bed. Comparison of the conventional reference measurements with the cross-correlation velocities show that the correlation method has the potential to provide reliable measurements of near-bed current profiles. |
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