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    A multi-frequency method for improved accuracy and precision of in situ target strength measurements

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    Document Number:
    WG-EMM-97/24
    Author(s):
    Hewitt, R.P., Soule, M.A., Demer, D.A.
    Agenda Item(s)
    Abstract

    The effectiveness of a split-beam echosounder system to delineate single scatterers and accurately measure in-situ target strengths (TS) is dramatically enhanced (98.2 -99.4%) by combining synchronized signals from two or more adjacent split-beam transducers of different frequencies. The accuracy of the method was determined through controlled test tank experiments using multiple standard spheres and 38 and 120 kHz split-beam transducers. Furthermore, by utilizing the angular position information from one of the split-beam transducers, additional corresponding TS measurements can be collected with juxtaposed single-beam transducers. Both methods were utilized to extract in-situ TS measurements of Antarctic scatterers simultaneously at 38, 120, and 200 kHz. Differences in the resulting TS measurements provided information about the identity of constituents in a mixed species assembly.

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