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Seafloor characterization based on multibeam backscatter data

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Beyer, A. , Chakraborty, B. and Schenke, H. W. (2004): Seafloor characterization based on multibeam backscatter data , 7th European Conference on Underwater Acoustics, ECUA 2004, Delft, The NetherlandsJuly .
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Multibeam echo sounders can be used as a remote sensing tool to investigate the seafloor. Angular backscatter data is used to gain information from the acoustic pulses in addition to the depth measurements and provide a tool to investigate the seafloor cover. The presented approach aims to segment and characterize seafloor regions into facies of different acoustic properties. The identified acoustic facies also indicate a change of sediment properties. Based on this information the spatial validity of surface samples (e.g. multicorer) can be determined.In addition to the depth measurements, Hydrosweep DS2 multibeam system provides beamwise amplitude information of the received echo signal. The amplitudes are converted into multibeam backscatter strength using the NRGCOR software. After removing the mean angular backscatter decrease from the data, shape invariant backscatter is derived and used to generate backscatter grey scale maps. Thereafter, seafloor areas of different grey scale levels are separated. These areas are characterized based on shape invariant backscatter level, slope of the angular backscatter decrease, mean angular response at 20 degrees incidence angle and coefficient of variation. Since shape invariant backscatter data are related to one reference incidence angle, they are suitable for display on bathymetric maps. Structures which are not visible in the bathymetry can be identified.Hydrosweep angular backscatter data has been used to identify and characterize different seafloor segments at the eastern margin of the Porcupine Seabight (northeast atlantic). Channels, carbonate mounds and buried mounds are analysed to distinguish seafloor facies. The range of the shape invariant backscatter grey level is 12dB. The backscatter levels are higher for the mound area compared to the channel seafloor. The buried mounds show the highest slope of the angular backscatter descrease. The coefficient of variation is highest for the mound areas.

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