HYDROACOUSTICS
ANNUAL JOURNAL |
START | NEW VOL 20 | SEARCH | STATISTICS | PAS - GDANSK DIVISION |
pp. 135-142, vol. 14, 2011 Zbigniew Łubniewski Gdańsk University of Technology, Department of Geoinformatics, Gdansk, Poland Key words: bathymetry; seafloor characterisation; signal and image processing; Gulf of Gdansk Abstract: In the paper, the approach to seafloor characterisation is presented. The multibeam sonars, besides their well verified and widely used applications like high resolution bathymetry and
underwater object detection and imaging, are also the promising tool in seafloor characterization
and classification, having several advantages over conventional single beam echosounders. The
proposed approach relies on the combined, concurrent use of several techniques of multibeam
sonar data processing. The first one is based on constructing the grey-level sonar images of seabed
using the backscattering strength calculated for the echoes received in the consecutive beams.
Then, the set of parameters describing the local region of sonar image is calculated. These include
both the first and the second order statistics of the grey level, and the texture analysis. The second
technique utilises the 3D model of the seabed surface, which is constructed as a set of (x, y, z)
points using the detected bottom range for each beam in the multibeam system seafloor imaging
procedure. For the local region of seabed surface, the descriptors like rms height and
autocorrelation radius are calculated. The third technique assumes the use of a set of parameters
of the multibeam echo envelope, similarly as in single beam classification. The parameters include
echo energy and its statistics, as well as the set of echo shape descriptors, and are calculated for
each beam allowing the estimation of their dependence on seafloor incident angle. Then, for
selected parameters, the characteristic features quantitatively describing their angular
dependence, like slope, or range, are calculated. Finally, the features obtained by these
3 techniques have been combined together and used in seabed supervised classification procedure
based on standard classifiers. The proposed method has been tested using multibeam data records
acquired from several bottom types in the Gulf of Gdańsk region. The obtained results show that
application of the proposed combined approach improves the classification performance in
comparison with those of using only the one scheme of seafloor multibeam data processing.
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