An Observing System for Canadian Arctic Ice Caps

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An Observing System for Canadian Arctic Ice Caps

• Martin Sharp
• Earth and Atmospheric Sciences
• University of Alberta

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Queen Elizabeth Islands 110,000 km2 ice
Grant
Agassiz
Muller
Likely to respond more quickly than Greenland
ice sheet (response times on order of centuries
to a millennium)
Prince of Wales
Steacie
Sydkap
Manson
Behaviour very poorly known
Devon
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• The Arctic climate is changing and is expected to
  continue to change

Mean Annual Air Temperature 2060-2089 c.f.
1961-1990 Source Polar Research Group, U.Illinois
Arctic Annual Temperature Trends
1954-2003 Source J.Walsh
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The Problem

• Is the area and volume of Canadas Arctic
  glaciers and ice caps responding to these climate
  changes - and how rapidly ?
• What is the contribution of these changes to
  global sea level?
• How important are the different mass loss
  processes - surface melt and iceberg calving?

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An Observing System

• Gradual development since 1994
• Modeled on PARCA - mix of remote sensing
  (airborne satellite), in situ observations and
  modeling
• Done with multiple increments of short term
  funding and few people
• Key differences from Greenland - scale of ice
  masses, max elevations (minimal dry snow zone),
  extensive surface melt, more complex topography

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What do we need to know?

• Ice extent - multiple epochs
• Surface elevation - multiple epochs
• Ice thickness and bed topography
• Surface velocity (and its temporal variability)
• Surface mass balance (including inter-annual
  variability)
• Iceberg calving flux

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Ice Extent

• Data sources 160k aerial photography (1959/60)
  and derived 1250k NTS maps (digital) Landsat7
  ETM and ASTER (1999-2004)
• Alternatives DISP (1960s), MODIS, LandSat
• Accuracy (line placement due to digitizing, snow,
  cloud, shadow masking) AP 5-75m ETM (15-120m)
• Problems
• N. Ellesmere not covered in recent period
• ice outline errors in NTS maps
• limited ground control for AP
• lack of knowledge of short term variability in
  calving front positions

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The Whole Picture
1960-1993 only
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Surface Elevation (1)

• Data sources
• CDED (based on 1250k NTS sheets and 1959/60 AP)
  
• 1995 2000 airborne data (Abdalati, Dowdeswell)
  
• GLAS (post 2003)
• Alternatives kinematic GPS from traverses,
  InSAR, ASTER
• Vertical Accuracy
• CDED - /-20-50m
• Abdalati (ATM) lt 0.1m
• Dowdeswell (radar terrain clearance and aircraft
  GPS) /- 7m
• GLAS lt0.15m
• InSAR 30-40m

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Surface Elevation (2)

• Issues
• Poor quality of 1959/60 data due to limited
  ground control and poor contrast above snowline
• limited airborne coverage (ATM often misses major
  outlet glaciers)
• spacing of GLAS orbits and limited of crossing
  points per ice cap (esp. in S)
• InSAR DEMs pick up subtle detail but have poor
  absolute accuracy
• only possible to detect large dynamically driven
  changes
• Needs improved ground control to redo
  photogrammetry (potential accuracy /- 5m) and
  improve absolute accuracy of InSAR DEMs more
  extensive ATM coverage

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IceSat Orbits Oct/Nov 2003
Devon Ice Cap CDED - GLAS 2003 NB Only 16 orbit
crossing points
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Ice Thickness and Bed Topography

• Data Sources Dowdeswell (2000) airborne RES
  (Devon, Manson, POW, Agassiz)
• Alternatives Older data (Robin, Clarke,
  Koerner) limited U.Kansas data (1995) flow
  model inversion
• Accuracy 8m at crossing points
• Issues
• No recent coverage for Axel, N.Ellesmere, Sydkap,
  smaller ice masses
• Limited to along flow line on outlet glaciers
• Only Devon has dense (10km) grid

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Other approaches inversion of numerical flow
models ?
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Surface Velocity

• Data sources ERS 1/2, RadarSat (InSAR/speckle
  tracking) Landsat 7 ETM, ASTER, AP (feature
  tracking/IMCORR)
• Alternatives balance velocities, static GPS,
  optical surveying
• Accuracy InSAR - lt 3 m/yr in interior regions, lt
  10 on outlets Speckle tracking - lt10 (but
  limited validation data) ImCorr - 1 pixel
  rectification error
• Issues
• InSAR - accuracy of external DEMs (CDED)
• poor coherence (time period between images, high
  outlet velocities)
• lack of ascending and descending orbit coverage
  (need to project look-direction velocities)
• seasonal variability unknown due to lack of
  summer coverage
• lack of time series
• lack of data for balance velocity calculations

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Surface Velocities from Interferometry and
Speckle Tracking
Balance Velocities
Devon Ice Cap Flow Field
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Surface Mass Balance

• Approach combine ice core analyses and modelling
• Problems
• upscaling/downscaling climate input data
  (ppt/temp)
• lack of on-ice temperature data
• poor knowledge of accumulation rate fields
• lack of validation data for models
• Issues Coarse resolution of passive microwave
  data limits use for melt detection and
  accumulation measurement on ice caps (lack of dry
  snow zone is also problematic for accumulation
  measurement)
• Possibilities QuikScat for facies mapping, melt
  detection and possibly melt intensity measurement
  (critical as inter-annual MB variability is
  mainly due to summer balance variability)

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Lapse Rate Issues
John Evans Glacier, Ellesmere Island Evolution of
surface air temperature field during 2002 melt
season
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Air temperature versus QuikScat
backscatter Station at 1300m, Leffert Glacier,
Prince of Wales Icefield, Ellesmere Island
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QuikScat - 2000-2004 Melt Duration Climatology
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2001 Warm year
2002 Cold Year
Lapse rate implications?
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Iceberg Calving Flux

• Approach compute from surface velocity and ice
  thickness at grounding line
• Problems
• poor InSAR coherence due to fast flow near
  grounding lines
• patchy data from ImCorr/feature tracking
• poor knowledge of temporal variability in
  velocity
• lack of cross-glacier thickness data near
  grounding line
• floating tongues not well known (bottom melt
  issue)

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Primary Needs (1)

• Improved ground control for topographic mapping
• Continued high resolution visible imagery for
  extent (Quickbird/Ikonos acquisition?)
• High accuracy surface topography for inversion
  modelling, balance velocities, volume-area
  scaling
• New thickness datasets, especially for Axel
  Heiberg and N.Ellesmere, and across outlet
  glacier grounding lines
• Targeted interferometry mission plus year-round
  GPS measurements on outlet glaciers
• Identify grounding lines and floating tongues

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Primary Needs (2)

• Extended net accumulation dataset from shallow
  ice cores
• compute balance velocity fields
• develop climatology
• understand patterns of inter-annual variability
• Explore potential of RCMs/GCMs for accumulation
  simulation
• Extend air temperature and summer melt
  measurements
• ground truth active microwave data
• understand lapse rate variability
• model validation
• Continued collection of high resolution active
  microwave data