c. vincent lgge/cnrs doris days 2-3 may 2000 toulouse, france. doris campaigns at dome concordia,...

C. VINCENT LGGE/CNRS DORIS DAYS 2-3 May 2000 Toulouse, France.

DORIS campaigns at Dome Concordia, Antarctica in 1993 and 1999-2000

C. Vincent1, JJ. Valette2, L. Soudarin2, JF. Crétaux3, B. Legresy3, F. Rémy3, A. Capra4

1 LGGE/CNRS, Laboratoire de Glaciologie et de Géophysique de l’Environnement, Grenoble, France2 CLS, Collecte Localisation Satellites, Ramonville, France3 LEGOS/GRGS (CNES/CNRS-UPS), Toulouse, France

4 Istituto de Topografia, Geodesia e Geofisica Mineraria, Universita de Bologna

DORIS DAYS 2-3 May 2000


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Concordia : French - Italian glaciological research project (LGGE/DISTART,...)

topics : snow accumulation, ice thickness, ice flowing …

EPICA : European project for deep ice coring

topics : ice cap response to global climate changes,

north-south hemisphere coupling...

Base on the Antarctic continent

open from December to February since 1996,

permanent by 2003

Management by IFRTP


Why a drilling location there?

Interests of this continental dome :

T < -25°C, no summer ice melting

excellent location for a whole Antarctic record

3300 m thickness long and continuous climate record 400 Ka

least disturbed ice sequence at the dome summit (minimal ice flow correction)


Main geodetic informations needed

Questions Technique

1996 Position of the dome summit ? ERS-1 altimeter (Rémy)

GPS (Ceffalo)Airbone VHF radar (Tabacco) for layering

2000 Absolute 3D ice surface velocity ? DORIS 1993 and 1999-2000 (C. Vincent)

local deformation ? GPS 1995-1998 (A. Capra)

ERS-1 Insar 1996 (B. Legrésy)


Charming but constraining place (1)

Equipment suffering :

beacon specification from -20° to +55°Cgradient < 10°/hr

Generator failures USO drift of a few 10-11/jr

(still under specification)


Charming but constraining place (2)

Scientist suffering :

Dry but freezing summertime(4 g/cm2 equivalent water a year)

What geodetic « monumentation » ?How to prevent from stake subsidence?

How to measure snow accumulation ?


CLS DORIS Data Processing Center, Toulouse

Onboard instrument controlTelemetry acquisition and preprocessingOperational orbit and stations position (48 h delay)

Spot 4 data validation

2 days delay Dome C operational location (height)


DORIS campaigns

1993 : 16 days (11/26 – 12/5)SPOT 2

85 pass. / 2097 obs.

1999-2000 : 27 days (12/8 – 1 /2)SPOT 2 and 4

498 pass./ 13164 obs.

DORIS observations at main point (D1)

Drilling siteD1 Doris main site (IERS id. : 66009 in 93 - 66013 in 99)D2 Doris ancillary site (66014)

10 km5 m isolines


Data processing

At GRGS/CLS DORIS data analysis center for IERS and IDS

with GINS/DYNAMO software

and the most recent models : GRIM5 (Biancale et al.), atmospheric effects

Geodetic parameters : satellites orbit, stations position and velocity

Empirical coefficients : air drag, solar pressure radiation, Hill residual forces, zenital tropospheric delay

Instrumental parameters : USO frequency bias


Absolute velocity corrections

Antarctic plate tectonic motion deduced from DORIS at Dome Concordia :

in latitude : -9.4 mm/yr

in longitude : 0.4 mm/yr

(Crétaux et al. 1998)

Post glacial rebound uplift : less than 1-3 mm/yr

Titre:GMT v3.0 Document from pscoastAuteur:laurent soudarin grgs p 62925Aperçu:Cette image EPS n'a pas été enregistréeavec un aperçu intégré.Commentaires:Cette image EPS peut être imprimée sur uneimprimante PostScript mais pas surun autre type d'imprimante.


Preliminary DORIS results

2 months global network solutions (Nov-Dec 93 and 99)

Typical precision :

7 parameters Helmert transformation (versus solution 1993)

3D coordinates changes over 6 years(same réf. point, plate motion is removed)

1 satellite 2 satellites

Permanent station 2 cm 1 cm

Dome C 3 cm (1993) 1.5 cm (1999)

Latitude Longitude Height

- 3.6 cm - 10.8 cm -57.4 cm


Contribution to ice core analysis (1)

DORIS 3D absolute velocity gives an input for numerical ice flow model in depth. Essential for cores dating.

DORIS results in horizontal : 0.6 cm/yr in latitude

-1.8 cm/yr in longitude

agree with

balance model between snow accumulation and

ice flow induced by gravity (figure)

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(Legresy)


Contribution to ice core analysis (2)

DORIS results in vertical : -9.6 cm/yr

Probably the first absolute determination of the vertical velocity

observed snow accumulation at the top of the stake (height level change) : 35 cm over the 6 years while 10 cm/yr is expected (Petit et al.)

Error observation or snowfall anomaly ?

Mass balance between snowfall and ice flow towards the ocean ?

Sea level and climat changes implications


Contribution to radar remote sensing observations

SAR Interferometry maps relative surface velocity in the line of sightERS SAR interferogram (69 days interval) shows maximum of 3 cm/yr

DORIS gives the absolute ITRF tie of the velocity fields

Space Radar Altimetry maps ice topography within 10-20 cmbut an in-situ calibration is needed,

moreover the signal penetration depends on the snow structure

DORIS gives the height reference and its variations in time


Conclusions

DORIS (93-99) component of CONCORDIA project confirms that a very low absolute horizontal ice surface velocity affects the EPICA drilling (< 2 cm/yr). Also vertical flow determination as a first.

DORIS absolute geodetic approach fully completes GPS survey and calibrates radar satellite remote sensing techniques (with future missions ERS2, ENVISAT, IceSat, CRYOSAT).

Proposal to IDS for repeated DORIS campaigns at Dome Concordia

c. vincent lgge/cnrs doris days 2-3 may 2000 toulouse, france. doris campaigns at dome concordia,...

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