outline use of satellite altimetry for oceanography operational oceanography – godae - mercator

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003

From altimetry to operational oceanography, need for a precise geoid. Exemple of the E.U. GOCINA

Project.

OutlineOutline

Use of satellite altimetry for oceanographyUse of satellite altimetry for oceanographyOperational oceanography – GODAE - MERCATOROperational oceanography – GODAE - MERCATORMean dynamic topography (absolute dynamic topography): the Mean dynamic topography (absolute dynamic topography): the

presentpresentConclusions - perspectives for GOCEConclusions - perspectives for GOCEThe GOCINA projectThe GOCINA project

Fabrice Hernandez and P.Y. Le Traon

CLS Space Oceanography Division

+ GOCINA consortium


Absolute dynamic topography from altimetry (1)

1. Estimate a mean dynamic topography (< >) from GOCE , altimetry or other:• difference between MSS and geoid• climatology from in situ data, or synthetic geoid product• ocean model mean

The mean should correspond to a mean over a precise time period determined by the sea level anomaly calculation (typically several years or the duration of an altimetric mission). The longer is the time period, the better as the scales of the mean signal will be larger.

2. Add this mean dynamic topography to sea level anomaly ( ') derived from repeat-track analysis.

One of the main objectives of GOCE is to provide a sufficiently accurate geoid to allow a precise estimation of absolute dynamic topography from altimetry.

In practice the best procedure to get an estimation of the absolute dynamic topography (and its error) ( = < > + ') from altimetry will be :

9993h G

9993η

’= h ’

G

h + G

h’= h - 9993h

9993h

9993η


Absolute dynamic topography from altimetry (2)

This product will have a major impact on scientific and operational applications (e.g. GODAE, MERCATOR) of satellite altimetry (e.g. Woodworth et al., 1998; Le Provost et al.,1999) :

•better interpretation of altimeter signals (absolute dynamic topography): Sea level monitoring and climate studies…

•comparison/combination with in-situ data

•general circulation and heat transport

•data assimilation and ocean forecasting

•...

The (main) product that oceanographers will need from GOCE will thus be a mean dynamic topography (and its error)


Operational oceanography

The GODAE vision

"A global system of observations, communications, modelling and assimilation, that will deliver regular, comprehensive information on the state of the oceans, in a way that will

promote and engender wide utility and availability of this resource for maximum benefit to the community”

(GODAE Strategic Plan, 2001)


The Global Oceanic Data Assimilation Experiment

Objective: To provide a practical demonstration of real-time operationaloperational global oceanography

Regular comprehensive description of the ocean circulation at high temporal and spatial resolution

Consistent with a suite of remote and in-situ measurements and appropriate dynamical and physical constraints

Climate and seasonal forecasting, marine safety, fisheries, the offshore industry, Navy applications and management of shelf/coastal areas are

among the expected beneficiaries of GODAE

The integrated description of the ocean that GODAE will provide will also

be highly beneficial to the research community

Includes the main operational and research institutions from Australia, Japan, United States, United Kingdom, France and Norway

Main demonstration phase : 2003 to 2005 (prototypes are already running)

GODAE


Planned GODAE system

Modeling and Assimilation

In 2003, the modeling/assimilation unit of theMERCATOR system is based on two components :

• a high resolution (1/15°) NorthAtlantic model, including theMediterranean sea

• an intermediate resolution(1/4°) Global Ocean model

Common boundary :9° N Atlantic


Forecasts for May 14,

2003

SSH

2003: the second MERCATORPrototype : PSY2

Mixed layer depth


3000 floats providing T and S profiles (0-2000 m) every

10 days and measuring velocity at 2000 m =

• vertical description• large scale and seasonal variations • water masses• improved estimation of absolute mean dynamic topography (a few cm rms)• …


SSALTO/DUACS (CLS/CNES) : Real time processing of TOPEX/POSEIDON, ERS-1/2, GFO, Jason-1 and ENVISAT

Real time processing (2-3 days)

Global crossover minimizations, inverse techniques to remove long wavelength errors => high accuracy SSH (Sea Surface Height) data

Consistent mean profiles to reference multiple altimeter data => consistent SLA (Sea Level Anomaly) data

Products directly useable for scientific and operational applications (climate and mesoscale)

Real time processing of T/P and ERS-2 data during the 1998 El Nino

Serving operational oceanography (GODAE) and climate forecasting centers

Mesoscale to climate, surface integrated circulation

Meeting French Ressources Organization for GOCE Paris, the 14th of may, 2003 SSALTO/DUACS : High resolution from T/P, ERS-2 and GFO data

+ synthetic mean dynamic topography

Need for operational oceanography:

Maps of SLA can be produced with a good accuracy (better than 5cm and 10 cm/s) and describe scales shorter than 100 km and 5 days.

The (main) product that oceanographers will need from GOCE will thus be a mean dynamic topography (and its error) at equivalent scale and accuracy !


Mean Dynamic Topography from POCM, Levitus and

EGM96-MSS

rms differences are about 12 cm (wavelengths > 2000 km)

POCM

EGM96 - MSS

Levitus (700 m)


m

m

MSS CLS01 – EIGEN2

Levitus (700 m)

OCCAM


Mean Dynamic Topography (conclusion…)

• Improvements needed in both accuracy and resolution…•Based on CHAMP, GRACE, GOCE (large and medium scales), in-situ data and models (shortest scales, and consistent physics)•Homogeneous period•...


Improvement in the 7-day sea level anomaly forecast due to the use of a “GCE” MDT (Dombrowsky, 1999). Units from 0 to 50 cm2

Use of a “GOCE” MDT allow a better prediction of the eddy field, by about

15% of the signal variance for a 7-day prediction.

2-week forecast error with “GOCE” MDT is equivalent to 1-week forecast

error with “today” MDT

This improvement will come in addition to the improvement in the knowledge of

the mean circulation itself.

The effect should be larger for longer term forecast

Need for operational oceanography: Impact of GOCE and high accuracy MDT


Impact of the Synthetic MDT (Rio, 2003) in MERCATOR

Synthetic MDT MERCATOR MDT Difference

• More realistic (comparison to drifter, hydrographic observations)

• Enhance the forecasting capability of the system?


MKE comparison (cm2/s2): stronger mean currents. Subpolar gyre better defined

6 months of the impact experiment (operational configuration … Sept 01 to April 02)



EKE comparison (cm2/s2): intensification of the model mesoscale variability

6 months of the impact experiment (operational configuration … Sept 01 to April 02)



The GOCINA project (5th E.U. FP)http://www.gocina.dk/

Geoid and Ocean Circulation in the North Atlantic

GOCINA will develop generic tools to enhance ocean analysis using Earth observation data from ENVISAT and GOCE. The project will examine the mass and heat exchange across the Greenland-Scotland Ridge. This analysis will give invaluable information on the ocean role in climate. The project will in particular support the GOCE mission with a set of specific recommendation for integrating GOCE in ocean circulation studies and an accurate geoid model for validation purposes.

A major task is to determine an accurate geoid in the region between Greenland and the UK and, thereby, create a platform for validation of future GOCE Level 2 data and higher order scientific products. The new and accurate geoid is used together with an accurate mean sea surface to determine the mean dynamic topography. The mean dynamic topography is used for improved analysis of the ocean circulation and transport through the straits between Greenland and the UK.

Gocina: 36 mois (11/2002 - 11/2005)




Partner 1 (KMS):Kort & MatrikelstyrelsenGeodetic Department, DK-2400 København Att: Per Knudsen (coordinator)Partner 2 (NMA):Norwegian Mapping AuthorityGeodetic Institute, N-3504 HønefossAtt: Dag SolheimPartner 3 (UEDIN):The University of EdinburghGeography and Geophysics, EH9 3JW EdinburghAtt: Roger HipkinPartner 4 (UREADES):University of ReadingEnvironmental Systems Science Centre, RG6 6AL ReadingAtt: Keith HainesPartner 5 (NERSC):Nansen Environmental andRemote Sensing CenterN-5059 BergenAtt: Johnny JohannessenPartner 6 (CLS):Collecte Localisation SatellitesSpace Oceanography Division,F-31526 Ramonville St. AgneAtt: Fabrice Hernandez

The partners each have a high international reputation for expertise relevant to their specific roles. KMS, NMA, and UEDIN have expertise in geodetic disciplines associated with geoid determination. UREADES, NERSC, and CLS have expertise in oceanographic disciplines associated with ocean circulation and data assimilation. KMS and CLS have expertise in processing satellite altimetry for both geodetic and oceanographic purposes.

Strong collaboration with OCTAS (Norway)

http://www.octas.statkart.no/




• WP1: Geoid determination (R. Forsberg/R. Hipkin)• Collect marine gravity data• Complete with air-borne gravity survey + intercalibration• Compute gravimetric geoid + errors using state-of-the-art method (marine, land, topo, airborne data) with the mgal precision• Take into account available CHAMP & GRACE data to enhance long wavelength

.




Airborne gravimetry (collaboration with

OCTAS)




WP2: Mean Sea Surface Determination (O. Andersen/F. Hernandez)• Compile satellite altimetry: T/P, Jason-1, ERS-1/2, EnviSat, Geosat, GFO up to 2002• Analyse existing MSS in the area (KMS01, CLS01, GSFC00.1)• Determine a high resolution MSS (1/60°)

.




WP3: Mean dynamic topography determination (K. Haines/F.Hernandez)

• Collect existing MDT (climatology, model, etc…) and evaluation• Compile in-situ data (hydrographic data, surface drifters etc…)• Determine a MDT from climatology• Determine a synthetic MDT• Determine a model MDT from OGCM .




WP4: Assessment and Validation (D. Solheim/A. Vest)• To assess the initial models residuals• Compare the different MDT to in-situ data• Infer error characteristics of the different models

.




hddynMDTMDTSLASLA EhEHE



Geoid and Ocean Circulation in the North AtlanticMDT = KMS-01 MSS - ”Tallinn”

geoid OCCAM

MDT = KMS-01 MSS – EGM96 geoid MDT = KMS-01 MSS – geoid36.eig




WP5: Technique integration (R. Hipkin)• Integrate the three quantities (MSS, MDT, geoid) and errors• Testing new techniques (data assimilation and geoid inversion) for calculating the best possible local solution• Investigate impact of the GOCE errors

WP6: Ocean circulation and transport (F. Hernandez/J. Johannessen)

• Testing the MDT in OGCMs (impact in mass and heat transport across the straits, outflow…)• Testing the predictability at seasonal/interannual scales (NAO prediction)

WP7: Recommendations for integrating GOCE (J. Johannessen)• Educate and prepare the community in using GOCE data for oceanography including sea level and climate research as well as operational prediction• Develop methods for generating regional gravity fields and use them to generate a best possible regional gravity field and geoid model for the North Atlantic that can be used in validation of the GOCE products

.




•… If GOCE is launched in 2006, the GOCINA would be finished, but conclusions could be applied

• GOCINA is a unique community (geodesy and oceanography) for calibration and validation

• Direct outcome and applications for several communities (climate prediction, ocean studies, operational oceanography, marine security and oil industry…)

outline use of satellite altimetry for oceanography operational oceanography – godae - mercator

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