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Side-scan sonarHabitat mapping and sediment
detection
Geological oceanographyRiikka Puntila
2.4.2008
How does it work?
• Sonar uses ultrasound which needs a medium, water, to progress
• Image is constructed of different reflections of different objects
• Sound frequencies vary from 100-500 kHz– High frequencies give better resolution but
smaller range
http://woodshole.er.usgs.gov/operations/sfmapping/sonar.htm
stones
sand
gravel
rock
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http://pubs.usgs.gov/fs/fs039-02/fs039-02.html
Side-scan as a tool
• Not very usable alone– Calibration, GPS etc.
• The scan results after calibration can be extrapolated in larger areas
• Useful tool when grain-size analysis, photographs, transects, other acoustic systems etc. are added
Cochrane and Lafferty 2002
Use of acoustic classification of sidescan
sonar datafor mapping benthic habitat
in the Northern ChannelIslands, California
Purpose
• To study usefulness of side-scan sonar in mapping the extension on suitable habitats for abalone and rockfish
• To assess size and boundaries for the protected area
• Data from this study is to be used in addition to depth, chemistry and circulation patterns
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Study area
Submersible ground-truthing
• Three distinct bottom types– Thick bioturbated
sand– Thin winnowed sand– Encrusted rock
Black:overlapping sand
Dark grey:bioturbated thick sand
Light grey:winnowed sand
White:encrusted rock
Conclusions
• The side-scan sonar picture was useful for distinguishing sand areas from rock
• In the far ends of the range interpretation was not certain
• This method helped to reveal far greater areas of sandy bottom than previous maps of the area Goff et al. 2000
Correlation of side-scan backscatter intensity with
grain-sizedistribution of shelf
sediments, New Jersey margin
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Purpose
• To study correlation between backscatter intensity and sediment grain-size– Quantitative interpretation
• To evaluate the accuracy of assumptions made in earlier study by Goff et al. 1999
Higher backscatter,
mobile sediments
Lower backscatter,
static sediments
Figure 2.
Figure 3.
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Conclusions
• In well sorted sediments a good level of correlation can be obtained
• The presence of unsorted sediments and in trimodal sediments mean grain size is not representative
• Backscatter is the most sensitive to larger grain sizes
Conclusions&Discussion
• Side-scan sonar is a useful tool with some constraints– Other methods needed for calibration
• Sonar surveys can cover larger areas than traditional methods
• Multiple geological and ecological applications
Thanks, ya’ll!
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