Seafloor classification of the mound and channel provinces of the Porcupine Seabight: an application of the multibeam angular backscatter data |
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Authors: | Andreas Beyer Bishwajit Chakraborty Hans Werner Schenke |
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Institution: | (1) Alfred Wegener Institute for Polar and Marine Research, P.O. Box 120161, 27515 Bremerhaven, Gemany;(2) National Institute of Oceanography, Dona Paula, Goa, 403 004, India |
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Abstract: | In this study multibeam angular backscatter data acquired in the eastern slope of the Porcupine Seabight are analysed. Processing
of the angular backscatter data using the ‘NRGCOR’ software was made for 29 locations comprising different geological provinces
like: carbonate mounds, buried mounds, seafloor channels, and inter-channel areas. A detailed methodology is developed to
produce a map of angle-invariant (normalized) backscatter data by correcting the local angular backscatter values. The present
paper involves detailed processing steps and related technical aspects of the normalization approach. The presented angle-invariant
backscatter map possesses 12 dB dynamic range in terms of grey scale. A clear distinction is seen between the mound dominated
northern area (Belgica province) and the Gollum channel seafloor at the southern end of the site. Qualitative analyses of
the calculated mean backscatter values i.e., grey scale levels, utilizing angle-invariant backscatter data generally indicate
backscatter values are highest (lighter grey scale) in the mound areas followed by buried mounds. The backscatter values are
lowest in the inter-channel areas (lowest grey scale level). Moderate backscatter values (medium grey level) are observed
from the Gollum and Kings channel data, and significant variability within the channel seafloor provinces. The segmentation
of the channel seafloor provinces are made based on the computed grey scale levels for further analyses based on the angular
backscatter strength. Three major parameters are utilized to classify four different seafloor provinces of the Porcupine Seabight
by employing a semi-empirical method to analyse multibeam angular backscatter data. The predicted backscatter response which
has been computed at 20° is the highest for the mound areas. The coefficient of variation (CV) of the mean backscatter response
is also the highest for the mound areas. Interestingly, the slope value of the buried mound areas are found to be the highest.
However, the channel seafloor of moderate backscatter response presents the lowest slope and CV values. A critical examination
of the inter-channel areas indicates less variability within the estimated three parameters. Financial support of this study
was granted by the European Commission Fifth Framework Project GEOMOUND (contract no. EVK3-CT-1999-00016). |
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Keywords: | Multibeam sonar Angular backscatter Carbonate mounds Seafloor channels Porcupine Seabight |
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