mapping the total antarctic ice sheet discharge: an ipy benchmark data set
DESCRIPTION
Mapping the Total Antarctic Ice Sheet Discharge: an IPY Benchmark Data Set. Robert Bindschadler Hyeungu Choi. IPY project #88 : Antarctic Surface Accumulation and Ice Discharge. Surface Accumulation Re: ITASE Ice Discharge Across grounding line perimeter - PowerPoint PPT PresentationTRANSCRIPT
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Mapping the Total Antarctic Ice Sheet Discharge: an IPY
Benchmark Data Set
Robert Bindschadler
Hyeungu Choi
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IPY project #88: Antarctic Surface Accumulation and Ice Discharge
Surface Accumulation• Re: ITASE
Ice Discharge• Across grounding line perimeter• Requires ice thickness and column-
averaged velocity
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Is monitoring outlet glaciers enough?
Rignot and Thomas assessed discharge from 33 outlet glaciers, including 25 of the 30 largest
Total accumulation = 814 Gt/a
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What’s Missing
• Coastal basins– Small areal
percentage (~25%)– High accumulation– Most of the perimeter
• Rignot and Thomas’ basins account for less than half of total accumulation flux (1811 Gt/a)
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Not a new idea
• Long-standing SCAR initiatives– ISMASS– GLOCHANT
• Even IPY couldn’t muster the necessary traditional tools– Airborne radar sounders
• A new approach was needed
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Space-based Approach
1. Delineate grounding line– Visual inspection of optical imagery– Tidal flexure in both GLAS and interferometric SAR (InSAR)
2. Determine elevation in vicinity of grounding line– Photoclinometry using GLAS elevation control and Landsat
image brightness
3. Convert grounding line elevation to ice thickness– Apply hydrostatic equilibrium condition
4. Multiply ice thickness by column-averaged velocity– InSAR – Surface velocity equals column-average for floating ice– Elevation values improve determination of velocity vector from
single track InSAR
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Trial Study
Landsat-5 images collected December 1986
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Grounding Line Delineation
Antarctic Digital Database
USGS Coastal Change Atlas
MODIS Mosaic of Antarctica
Our Study
Not shown
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Cloud-free GLAS data
Repeat groundtracks
70-m footprints spaced 175 m apart along-track
Approximately 11 km between groundtracks at 70oS
Frequent data loss near coast due to clouds
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Photoclinometry
• Assumes a diffusive surface of constant albedo
BADN cos
surface
imagebrightness
scalingcoefficient
surfaceslope
scattering
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Elevation Map
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Test Profile
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Test Profile
0
50
100
150
200
250
300
350
400
450
1 51 101 151 201 251
Pixe l Num ber (30 m eter interval)
Ele
vati
o (
met
ers)
Photoclinometry
GLAS Test
Control #1
Control #2
1
2
t
Ele
vatio
n (m
)
0
200
400
0 84
Distance (km)
1
t
2
1
2
t
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Grounding Line Thickness
0
20
40
60
80
100
120
140
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Pixel Number (30 m per pixel)
Ele
va
tio
n (
m)
0 13545 90Distance (km)
Ele
vatio
n (m
)
100
0
icewater
airicesurfacewater hZH
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Surface Velocity
dssVnsHQ )(ˆ)(
Interferometric analysis of SAR data is the primary source
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InSAR Velocity “Issues”
• Slow moving regions sometimes assumed stagnant to unwrap fringes
• Elevation data needed to convert single track InSAR data to surface parallel velocity– Improved elevations produced from photoclinometry can
improve existing velocity fields near grounding line
• InSAR reduction sensitive to tidal motions on floating ice– Can help determine grounding line
Aim is to produce and compile the most comprehensive set of Antarctic surface velocities
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More Unwelcome Details
• GLAS, Landsat-7 and SAR data not cotemporaneous
• Photoclinometry is subject to other reflectance-modifying effects– Frost patches– Clouds– Fog– Crevasses
• Some segments of the coast do not have land-fed floating ice
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ASAID TeamNew Zealand
Wolfgang Rack and Bryan Storey/Gateway Antarctica (University of Canterbury)
Satellite data analysis Dronning Maud Land and Victoria Land
Russia Maxim Moskalevsky
Ice thickness data (most in BEDMAP) and remote sensing analysis
East Antarctica between 20oE and 55oE
UK David Vaughan, Hugh Corr and Richard Hindmarsh/BAS
Ice thickness data Pine Island Bay, Rutford Ice Stream, Antarctic Peninsula
UK Andrew Shepherd/SPRI
InSAR velocities Amundsen Sea, Antarctic Peninsula
US Ian Joughin/University of Washington
InSAR velocities Compilation and gaps (as needed)
US Eric Rignot/NASA InSAR velocities Amundsen Sea coast
US Ken Jezek/Ohio State University
InSAR velocities and grounding line positions
Much of the perimeter
US Laurie Padman/ ESR
Tidal models Where needed
US Malcolm LeCompte/Elizabeth City State University
Satellite data analysis Where needed
US Prasad Gogineni/CReSIS
Ice thickness data West Antarctica (100oW to 110oW)
Country Colleague/ Institution
Nature of contribution Area covered
Australia Neal Young/ACE-CRC and Australian Antarctic Division
Grounding line (Landsat) and RES data
Wilkes Land coast (w/Italy) (43oE to 162oE)
France Emmanuel LeMeur/LGGE
Ice thickness (proposal pending) w/ Italy
Adelie Coast (137oE to 142oE)
Germany Daniel Steinhage/Alfred Wegener Institute
Ice thickness Filchner Ice Shelf to Shirase Gl. (35oW to 37oE)
Italy Ignazio Tabacco/University of Milan;Massimo Frezzotti/ENEA - CRE Casaccia
Field RES data and satellite data analysis
Scott Coast (165oE) to Porpoise Bay (128oE) and remainder of Wilkes Land coast (43oE to 128oE) w/Australia
Japan Makoto Omura/Kochi Women's University; Kazuo Shibuya and Koichiro Doi/ NIPR
Grounding line and InSAR velocities (including new ALOS and PALSAR data)
25oW to 40oEand where needed
New Zealand
Nancy Bertler/Victoria University
Glacier Ice Thicknesses Victoria Land (McMurdo vicinity)
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Summary
• Coastal catchments are a major component of Antarctic mass balance
• New methods work and data exist to quantify their contribution
• IPY is an excellent time to accomplish this task • Benchmark data sets of:
– Elevation (near grounding line)– Grounding line position– Grounding line thickness– Surface velocity– Discharge flux
• Proposal(s) pending
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Thank you!
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Backup
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Elevation Mapping
• Rotate image to align with Sun• Interpolate GLAS data to a continuous elevation
profile• For each pixel along grounding line, find nearest
GLAS profile up-sun and down-sun• Use GLAS elevations to determine
photoclinometry scaling coefficient l
ll
DNA
cos
• Determine elevation profile at each pixel between GLAS control elevations
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IPY Criteria
• Benchmark data sets
• Large international team
• Including students
• Data availability and archiving