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• Requires ice thickness and column-

averaged velocity

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

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)

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

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

Trial Study

Landsat-5 images collected December 1986

Grounding Line Delineation

Antarctic Digital Database

USGS Coastal Change Atlas

MODIS Mosaic of Antarctica

Our Study

Not shown

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

Photoclinometry

• Assumes a diffusive surface of constant albedo

BADN cos

surface

imagebrightness

scalingcoefficient

surfaceslope

scattering

Elevation Map

Test Profile

Test Profile

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1 51 101 151 201 251

Pixe l Num ber (30 m eter interval)

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Photoclinometry

GLAS Test

Control #1

Control #2

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)

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Distance (km)

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0 13545 90Distance (km)

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icewater

airicesurfacewater hZH

Surface Velocity

dssVnsHQ )(ˆ)(

Interferometric analysis of SAR data is the primary source

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

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

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)

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

Thank you!

Backup

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

IPY Criteria

• Benchmark data sets

• Large international team

• Including students

• Data availability and archiving