Finding the needle in the hay stack - tracing seabed gas seepages using hullborne multibeam echo sounder, and AUV based sonar and optical systems case study

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Scientific objective
A better understanding of the shallow geological systems in the Barents Sea with particular attention to fluid flow

Specific objectives

  • Identify regional spatial distribution of gas flares within an area of 3000 km2 in the Barents Sea
  • Identify and describe associated structures (i.e. pockmarks, carbonate reefs) using geomorphology
  • Document associated structures with visual tools
  • Determine present activity (gas bubbling, bacterial mats)
  • Sample seep related material (crusts, gas, mats sediments)

AUVs - platform for a range of instruments

  • Multibeam echosounder
  • Traditional sidescan sonar
  • Synthetic Aperture Sonar
  • Photo system – e.g. Tfish b&w photos
  • Methane sniffer
  • Other environmental sensors, such as Temperature, Salinity, Turbidity

Synthetic Aperture Sonar- HiSAS

  • Range-independent resolution
  • 5x5 cm – 2x180 m swath
  • Max resolution – 2x2 cm
  • 60 Gb/hr
  • Coverage 2 km2/hr
  • Bathymetry
  • Conclusions and experiences
  • Multi-scale approach: Hullborne MBE – AUV with HiSAS and Tfish - ROV
  • Water column data indicates gas flares (beware of fish shoals!)
  • Note – gas flares are episodic events – on and off
  • Hullborne MBE data give too low resolution for identifying seep-related structures
  • HiSAS may, or may not, identify carbonate crust structures
  • Visual documentation is necessary to verify carbonate crust structures, and related phenomena like depressions with algal mats

Sampling carbonate crusts with grabs and box corers is challenging – ROV… Combination of hullborne hi-res acoustic tools with AUVs fitted with dedicated sensors provides excellent opportunities to increase the scientific understanding of shallow geological processes, and for more applied investigations related to natural or anthropogenic gas seepages

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