Direct-Path Backscatter Measurements Along the Main Reverberation Track of TREX13

The primary goal of the Target and Reverberation Experiment in spring 2013 (TREX13) was to identify the major physical mechanisms responsible for midfrequency reverberation. While both the sea surface and seafloor can contribute to reverberation, the seafloor is typically dominant in shallow water e...

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Bibliographic Details
Published in:IEEE journal of oceanic engineering 2019-10, Vol.44 (4), p.972-983
Main Authors: Tang, Dajun, Hefner, Brian T., Jackson, Darrell R.
Format: Article
Language:English
Subjects:
Acoustic scattering
Backscatter
Backscattering
Boats
Dependence
Environment models
Experiments
Grazing
Ocean floor
Reflectance
Reverberation
Ridges
Roughness
Scattering
Sea measurements
Sea surface
sediment acoustics
Sediment composition
Sediments
Shallow water
Storms
Target and Reverberation Experiment 2013 (TREX13)
Variation
volume scattering
Water depth
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Summary:The primary goal of the Target and Reverberation Experiment in spring 2013 (TREX13) was to identify the major physical mechanisms responsible for midfrequency reverberation. While both the sea surface and seafloor can contribute to reverberation, the seafloor is typically dominant in shallow water environments. To determine the level of this contribution at the TREX13 site, the bottom backscatter sonar (BBS) was deployed from a dive boat at multiple locations around the site. The BBS consists of a source and a receiver mounted on a short bracket that is suspended above the seafloor to measure direct-path bottom backscatter at 3 kHz. Data near normal incidence were interpreted as bottom reflectivity, which was used to quantitatively explain the range-dependence of the sediment composition at the experiment site. Two factors restricted the estimates of the bottom backscatter strength to the minimum grazing angle of 21°: the currents at the experiment site made it difficult to position the system close to the seafloor, and the shallow water depth resulted in sea surface scatter contaminating small angle bottom backscatter. From the measured backscatter strength and by utilizing available environmental data, initial models of scattering strength indicate that at the shallow grazing angles of importance to reverberation, the scattering on the sand ridges is dominated by roughness scattering while in the muddy areas of the ridge swales, volume scattering dominates. The volume scattering from these mud areas is significantly stronger than the roughness scattering on the ridges by as much as 10 dB and may explain the substantial fluctuations observed in the reverberation as a function of range.
ISSN:0364-9059
1558-1691
DOI:10.1109/JOE.2019.2901425