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Sea ice thickness from CryoSat – A new data set for operational ice services?. Christian Haas German CryoSat Office AWI. First Earth Opportunity Mission, to be launched in November 2004. - PowerPoint PPT Presentation
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Sea ice thickness from CryoSat –
A new data set for operational ice
services?
Christian HaasGerman CryoSat Office
AWI
• Goals: 1. Observe changes in Arctic multi-year ice thickness2. Observe changes of Antarctic and Greenland ice
sheet thickness
• First Earth Opportunity Mission, to be launched in November 2004
• Radar altimetry mission with new technology: Synthetic Aperture, Interferometric Radar Altimeter: SIRAL
• Selected after 1999 proposal from European Scientists Group, lead by Prof. D. Wingham, University Collage London, UK
h?h?
Sea Ice
Ice Sheets
a
f
hi fw
(w i )
hss
(w i )
a
f
dhi
hs snow
ice
water
s
i
w
• Estimate Freeboard above Interpolated Ocean surface
• Conversion assumes reflection from the ice/snow interface
• Conversion to thickness using climatology of snow depth/densities [Warren, 1999]
Freeboard to Thickness Conversion
Observed thickness trends (ERS-2)(Laxon et al., 2003)
Comparison of satellite and submarine thickness measurements ‘93 to ‘97
Pulse-Limited Radar Altimetry
Time = 2*h/v
h
Oce
anIc
e S
heet
sS
ea I
ce
SIRAL: Synthetic-Aperture Interferometric Radar Altimeter
SAR
InSAR
250 m along track resolution
SAR / InSAR / LBR Modes
Orbit (Science Orbit):• 717 km Mean Altitude• 92° Inclination• 369 Days Repeat Cycle• 30 Days Subcycle• 7.5 km Inter-Track Spacing
at Equator
Nominal Ground Track of one Sub-Cycle
Cross-overs per 104 km2 per year
CryoSat Data Products
Level 0 - 1
Level1 - 1b
Level 2 - 3
Level 3 - 4
Level1b - 2
Coherent, Pulse-limitedRadar Echoes
CoherentSynthetic Beams
Multi-lookedBeams & Phases
Along-trackIce Elevations
Spatially &Temporally AveragedIce Thickness
Secular trendin ice thickness
~ 400 Gbit/day~ 3 Gbit/day
~ 20 Mbit/day
~ 1 Mbit/day
~20kbit/day
~ 400 Gbit/day
L0 - L1b Beam Formation & Steering
Doppler Beam Stack OverSpherical Surface
Level 1B Multi-looked Echoes
L0 - L1b Stack & Multi-looking
Simulated ‘SAR’ L1b - L2 Product
Conclusions• Major improvements over ice surfaces due to synthetic-
aperture interferometric (InSAR) processing• Data is orbit oriented (not imaging)• Low point-to-point covariance due to speckle Most
reliable for 104 km2 spatial / 1 month temporal resolution• Access to data through ESA Data-AOs• Uncertainties will be addressed by extensive validation
See you at: http://www.cryosat.de
Sea ice freeboard retrieval