Using ADV backscatter strength for measuring suspended cohesive sediment concentration

H. K. Ha, W. Y. Hsu, J. P.Y. Maa, Y. Y. Shao, C. W. Holland

    Research output: Contribution to journalArticlepeer-review

    74 Scopus citations

    Abstract

    Laboratory experiments were conducted at two institutes to reveal the relationship between acoustic backscatter strength and suspended sediment concentration (SSC). In total, three acoustic Doppler velocimeters (ADVs) with different frequencies (5, 10 and 16 MHz) were tested. Two different commercial clays and one natural sediment from Clay Bank site in the York River were checked for acoustic responses. The SSCs of selected sediments were artificially changed between a selected low and a high value in tap or de-ion water. Each ADV showed quite different backscatter responses depending on the sediment type and SSC. Not all devices had a good linear relationship between backscatter strength and SSC. Within a limited range of SSC, however, the backscatter strength can be well correlated with the SSC. Compared with optical backscattering sensor (OBS), the fluctuation of ADV backscatter signals was too noisy to be directly converted to the instantaneous changes of SSC due to high amplification ratio and small sampling volume. For the more accurate signal conversion for finding the fluctuation of SSC, the ensemble average should be applied to increase the signal-to-noise ratio. There are unexpected responses for the averaged backscatter wave strength: (1) high signals from small particles but low signals from large particles; and (2) two linear segments in calibration slope. These phenomena would be most likely caused by the different gain setting built in ADVs. The different acoustic responses to flocculation might also contribute somewhat if flocs are tightly packed. This study suggests that an ADV could be a useful instrument to estimate suspended cohesive sediment concentration and its fluctuation if the above concerns are clarified.

    Original languageEnglish (US)
    Pages (from-to)1310-1316
    Number of pages7
    JournalContinental Shelf Research
    Volume29
    Issue number10
    DOIs
    StatePublished - May 30 2009

    All Science Journal Classification (ASJC) codes

    • Oceanography
    • Aquatic Science
    • Geology

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