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