Observations of Arctic sea ice thickness and topography

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Observations of Arctic sea ice thickness and
topography
DAMTP, University of Cambridge

• Peter Wadhams
• Martin Doble
• Joao Rodrigues

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Research work at DAMTP

• Determination of Arctic sea ice thickness by
  upward-looking sonars mounted in submarines.
• Study of the topography of the ice underside by
  multibeam sonars mounted in submarines and AUVs.
• Sea ice thickness measurements using
  low-amplitude long period ocean waves.

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Basin-scale measurements of ice thickness by HMS
Tireless in 2004 and 2007
April 2004
March 2007
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Upward looking sonars

• Admiralty pattern 780 echo sounder
• Frequency 48kHz
• Beamwidth 3 degrees
• Records on paper chart, later digitized
• Admiralty pattern 2077
• Narrow beam digital system
• Coupled to the submarines inertial navigation
  system
• Coupled to a pressure transducer
• Effects of depth and speed variations are removed
  at source and a true record of draft vs distance
  is obtained directly

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Ice draft PDFs Tireless 2007
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Mean ice drafts 2004 vs 2007
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Mean ice drafts
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Multibeam sonar

• Kongsberg EM3002
• 256 narrow beams
• Swath of 150-200m for typical depths
• Ice draft obtained directly from the source
• First submarine-borne 3D sea ice data

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Recent AUV operations

• March 2007, Aplis ice camp, Beaufort Sea
• March 2008, Alert, Lincoln Sea

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APLIS, Beaufort Sea
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FY ridge photo-mosaic and sonar equivalent
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FY ice, rubble field, MY ice and ridge
MY
FY
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Refrozen lead
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Determination of ice thickness from long period
wave propagation

• Ocean waves propagate on the ice sheet
• Arrival times at specific locations measured by
  tiltmeters
• Dispersion relation vv(f,h) allows the
  determination of modal (or mean) ice thickness
  once v and f are known.

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Future work

• Likely Royal Navy submarine cruise in the spring
  of 2010.
• No AUV missions planned for 2009.
• Proposal to deploy a set of tiltmeter buoys
  equipped with high precision GPS in the Arctic
  Ocean.