Airborne sea ice thickness sounding
Stefan Hendricks1, Christian Haas2, Lasse Rabenstein1, John Lobach3
1. Alfred Wegener Institute for Polar and Marine Research, Germany
2. University of Alberta, Canada 3. Ferra Dynamics Inc., Canada
Sea Ice Physics
Stefan Hendricks
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Arctic Sea Ice
Arctic Sea Ice Minimum September 2007
Sea Ice Physics
Stefan Hendricks
Sea Ice Thickness Retrieval
CryoSat 2
ICESat
Local Scale
Regional Scale
Global Scale
Sea Ice Physics
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Principle: Frequency EM
Transmitter Coil Receiver Coil
Electrical Eddy Currents Conductive Medium
Electrical Insulator Primary Field
Secondary Field
Amplitude
Phase
Sea Ice Physics
Stefan Hendricks
EM: Application on Sea Ice
• High conductivity contrast between sea water & other media
• Conductivity in sea ice anisotropic (brine channels)
Sea Ice Physics
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Groundbased EM
• Standard instrument: Geonics EM31
Sea Ice Physics
Stefan Hendricks
EM Bird
Tx Laseraltimeter
GPS
Rx
Cx Bx
Length : 3.4m
Weight : 100 kg
Coil Separation : 2.7 m
Frequency : 3.68 (4.06) kHz Recording Frequency : 10 Hz
Operation Height : 10 – 15 m
Footprint : 40 – 50 m
Tx Transmitter Coil
Rx Receiver Coil
Bx Bucking Coil
Cx Calibration Coil
© Eric Brossier
Haas, 2007
Sea Ice Physics
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EM – Bird: Operations
Ship Based
Ice Camp
Various types of helicopters Land Based
Sea Ice Physics
Stefan Hendricks
EM Bird – Accuracy
• Instrument errors
– Noise
– Temperature changes – Pitch & Roll
• Other error sources
– Conductivity Variations (bottom melting)
– Sea Ice Porosity
• Over Level Ice
– Noise ± 5 cm – Accuracy ± 10 cm
Pfaffling, 2007 Haas et al., 2007
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• Footprint ~ 4 instrument altitude
• Smoothing of underice topography
• Underestimation of pressure ridge thickness ~ 50 %
3D Modelling: Comsol Multiphysics
EM Bird – Limitations
Sea Ice Physics
Stefan Hendricks
Sea Ice Thickness Transpolardrift
2004
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 PDF (m-1 )
2004 2001
1998 1996 1991
Sea Ice Physics
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IPY Cruise Arctic Ocean 2007
• IPY Polarstern Arctic Cruise Summer 2007
SPACE (Synoptic Pan-Arctic Climate and Enviroment Study)
Sea Ice Physics
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Transpolardrift - Summer 2007
Sea Ice Physics
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Variability of Thickness Pdf‘s
Sea Ice Physics
Stefan Hendricks
Sea Ice Thickness Transpolardrift (incl. 2007)
2004
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Comparison with Groundbased Methods
Biased by floe selection?
Biased by sea ice porosity?
Sea Ice Physics
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Retreat of Perennial Sea Ice
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Beaufort Sea
APLIS 2007 Ice Camp
SIZONet 2007/2008
APLIS
Barrow
Sea Ice Physics
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SIZONet 2008
5 4 3 2 1 0
Frequency (%)
12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2
Ice Thickness (m) 200804130010
10 8 6 4 2 0
Frequency (%)
12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2
200804122356
5 4 3 2 1 0
Frequency (%)
12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2
Ice Thickness (m) 200804141917
Sea Ice Physics
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SIZONet 2007/2008
Sea Ice Physics
Stefan Hendricks
Global Measurements
• Airborne EM applicable on the regional scale
• Limited in spatial & temporal coverage
– Logistics – Weather
• Global measurements only with satellites
• Measurements of freeboard height
– Laser/Radar
• Requirements
– Highly accurate elevation – Sea surface height
– Snow thickness
• Airborne EM + DGPS provides validation data
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EM Bird – Freeboard Retrieval
• Laser range correction with DGPS → Freeboard
GPS Altitude
Sea Ice Physics
Stefan Hendricks
Freeboard Characteristics
Thickness = R Snow Freeboard
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Conclusions
• Airborne EM provides a direct method to estimate sea ice thickness
• Field campaigns in the Arctic and Antarctic since 2001
• Results from the Arctic ocean in late summer 2007 confirms the retreat of thick perennial sea ice in the full thickness pdf
• DGPS data give additional information like laser freeboard
• Upcoming field campaigns this spring
– Laptev Sea – Lincoln Sea
Sea Ice Physics
Stefan Hendricks
Outlook
Polar Airplane : Polar 5
Total Pole Airship
Fixed Wing EM System
