WP3.1-ECOOP First annual meeting - Athens- 1 -

T3.1

Optimal synergy between altimetry and in-situ data

Claire Dufau (1)Enrique Alvarez (2), Ole B. Andersen (3), Florence Birol (4), Mathilde Cancet (4), Begona Perez (2), Gilles Larnicol (1), Gennady Koroatev (5),Per Knudsen (2), Arseny Kubryakov, Marie-Hélène

Rio (1)

(1)CLS, France(2) OPPE, Spain

(3) DNSC, Danemark(4) LEGOS-CTOH, France

(5) MHI, Ukrain

WP3.1-ECOOP First annual meeting - Athens- 2 -

T3.1 General objectives

• Consolidate and improve the altimeter products in regional/coastal areas

• Ensure the transfer of R&D activities to operation link with MERSEA project (open ocean)

link with ECOOP WP2 (operational demonstration)

• Two ECOOP regions are identified to lead specific R&D studies

– IBIROOS : CLS,LEGOS-CTOH,OPPE,DNSC– Black Sea : CLS,MHI

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Standard products are not really adapted for regional use, specially near the coast due to

– Specific dynamics over the continental shelves and shelf breaks show higher frequencies and shorter spatial scales

aliasing on lower frequencies disturbing signal quality – Lack of accuracy in the altimetry measure corrections essentially due to the

presence of land in the footprint of the sensor

First way of improvements– Better management of aliasing problem– Improvement of the corrections near the coast (atmospheric, geophysical, etc.)– Use of 20Hz sampling instead of 1Hz

Two Coastal Altimetry Projects have started in Europe to investigate such issues:PISTACH (CNES funded): since Autumn 2007, dedicated first to

Jason-2 products (launching in June 08)

COASTALT (ESA funded): since January 2008, dedicated first to ENVISAT products

Issues for Altimetry near the coasts

WP3.1-ECOOP First annual meeting - Athens- 4 -

Second way of improvements – Use of in-situ data located near the coast (Tide Gauges) for adding HF signal missing in

altimetry

0bjectives of T3.1:

– Analyze consistency between altimeter data sets and TG • HF signals • Tidal corrections• Measurement errors

– Estimate how HF signal in in-situ data could permit to improve altimetry

– Develop merging techniques

– Improve Mean Dynamic Topography in the Black Sea and IBIROOS

T3.1 Optimal synergy between altimetry and TG

WP3.1-ECOOP First annual meeting - Athens- 5 -

Production of a new regional altimeter dataset: the AVISO Black Sea product

Development of a regional multi-mission processing including

– a higher along-track resolution (no sub-sampling) than global products– adapted filtering & adapted long-wave errors correction– a new Mean Sea Level (performed with the latest SSH dataset including

new geophysical corrections )– a refined criterion for data selection – Smaller correlation scales for mapping (gridded products)

Global Regional

WP3.1-ECOOP First annual meeting - Athens- 6 -

A new regional altimeter dataset in Black Sea

Global product

Regional product

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Black Sea : first results of altimeter/in-situ comparison

8 coastal stations (TG) time series in 1993and 2 in 2003 (see besides)

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IBIROOS : altimetry & TG datasets

• Altimeter datasets : – 2 LEGOS-CTOH products

• With classical tidal correction (global model)• With regional tidal correction (regional model)

– 2 CLS (AVISO) SLA-extended products• the ones developed for MERSEA • their very new version (not yet available

though AVISO)

• Comparison period = 2003-2005

• In-situ data = Tide Gauges :– REDMAR network (provided by OPPE)– GLOSS/CLIVAR network (provided by CLS)– SONEL network– BODC network

WP3.1-ECOOP First annual meeting - Athens- 9 -

IBIROOS : How to compare them?

CORRELATIONS between the TG and altimetric sea level time series

• WP3.1 meeting on this topic in late December– Each partner has proposed some diagnostics that could be done such

as:

From a study made by LEGOS-CTOH over the NW Med Sea

From a study made by DNSC over the North Sea

WP3.1-ECOOP First annual meeting - Athens- 10 -

• WP3.1 meeting on this topic in late December– Each partner has proposed some diagnostics that could be done such

as:

IBIROOS : How to compare them?

Spectral Analysis (FFT) computed with TG and altimetric sea level time series

From a study made by LEGOS-CTOH over the NW Med Sea

WP3.1-ECOOP First annual meeting - Athens- 11 -

T3.1 next steps are:

• Performing altimetry & TG comparison studies over IBIROOS area– Datasets are just provided .. study is beginning.– Deadline = June 08

• Working on merging techniques between in-situ and altimetry data– Deadline = August 08

• Computing improved MDT for the 2 regions.– In progress– Deadline =August 08