satellite radar altimetry for monitoring caspian sea level changes

NATO ARW Ferrara December 2-4 1

Presented by

Consiglio Nazionale delle Ricerche, Italy

Lyard F., Roblou L., Cretaux F., Testut L., Calzas F. (LEGOS, France),Cipollini P., Snaith H., Venuti F. (National Oceanography Centre Southampton, UK) Kostianoy A., Sheremet N., Ginzburg A., Kuzmina E. (Shirshov Institute of Oceanology, Russia)Lebedev S., Sirota A., Medvedev D., Khlebnikova S. (Geophysical Institute, Russia)Mamedov R., Ismatova K., Alyev A., Nabiyev T. (Institute of Geography, Azerbaijan)

Contributors:

Stefano Vignudelli

Satellite ALTImetry for COastal REgions

Satellite radar altimetry for monitoring Caspiansea level changes

Lessons learned from the EU/INTAS ALTICORE project


Outline of my talk

Satellite Altimetry in few wordsOpen oceanCoastal zone

ALTICORE Project in a nutshellWho, what, where, how

Lesson learned in the Caspian SeaChallenges with sea level dataSome examplesPreliminary results from a pilot sea level station

Beyond ALTICOREInitiatives Summary – a personal view


R = ½ ct

S

η

GeoidG

Orbit

SSH

ReferenceEllipsoid

Satellite

Open OceanRadar Return Signal

Individual return signals are averaged on board (e.g. by 100 in Envisat)then trasmitted on ground at a rate, e.g. for Envisat of 18 hz (1/18 second of flight) which means measurements every 350 m along track but usually available (in open ocean) as averages over 1 second of flight, i.e. 7 km along track The Altimeter has low revisit (10 days and more)

How does satellite altimetry work ?

Satellite altimetry is success story in open ocean and next step is …

The Altimeter is nadir-poiting radar

Not Images but points along a track!

What are we measuring?


Coastal ZoneCoastal Zone, Inland Seas, Rivers, Sea Ice Areas

17 yrs multi-mission archiveNot fully exploitedNormally flagged as bad in the official products

Common technical issuesContamination of radar footprints Inadequacy of even failure of some auxiliary correctionsRe-thinking the quality control strategy

Meeting challenges in other areas

There is much interest in bring altimetry to the coastline

Not only for using in synergy with modelling tools and other data sources, but also to understand the error budget in global sea level rise when altimeters are tied to coastal tide gauges for calibration.

A hope at horizon: progresses in technology promise better resolution capability

New techniques (Delay-Doppler, Interferometry, Reflectometry) New concepts (Constellations)

Source: COASTALTEnvisat data

A good thing is that future sensors (AltiKa, WSOA, SIRAL on Cryosat, Sentinel-3 altimeter…) are being

designed with an eye to coastal zone


Some seminal papersCrout 1998 - could recover data when coastal topography is flatAnzenhofer et al. 1999 – retracking waveformsVignudelli et al. 2000 - Signal recovered consistent with in situ data

Started first program in 2001ALBICOCCA - ALtimeter-Based Investigations in COrsica, Capraia and Contiguous Area

NW Mediterranean proposed as the “operational lab” for coastal altimetryBackward reanalysis of standard products (1HZ i.e. 7 km)A revised post-processing strategy

Precursor of other projectsALTICORE (2007-2008)

to replicate in Caspian, Black, White, Barents, India and AfricaCOASTALT (2008 – now)

Focus on Envisat mission at 18 Hz (350 m)NW Med, Iberian and West Britain are the pilot sites

PISTACH (2007-2008)Focus on Jason missionGlobal coasts & inland waters

NASA OST ST call (2008-now)3 projects on “Coastal Ocean” and other three ones coastal-related

… & at centre of the communityRegular workshops

Silver Spring 2007, Pisa 2008, Frascati 2009, suggested Porto 2009) – see at www.coastalt.euSpringer Book

20 chapters, 70 people involved – see at www.alticore.eu/bookOne of the chapters is about Caspian Sea

Coastal Altimetry – a bit of story

More here today

http://www.coastalt.eu/

http://www.alticore.eu/book


Funded by EU under INTAS ProgramStarted on December 2006 for for a period of two years

Coordinating partner: Consiglio Nazionale delle Ricerche (Italy)

EU partners involved: National Oceanography Centre Southampton (UK) Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (France)

Three Eastern partners took part:P. P. Shirshov Institute of Oceanology (Russia) Geophysical Center (Russia)Institute of Geography (Azerbaijan)

Aiming atproviding altimeter data – more, better, closer coastsenhancing the capacity of Eastern partners to exploit data

This is done in a number of regional seasMediterranean, Black, Caspian, White, Barents

Three priority topics for action in the Caspian Sea:Getting the local information (e.g., in situ data, knowledge of metocean conditions, etc.)Improving the processing (editing, corrections, etc.)Making access to altimeter data easier

ALTICORE - Cooperation


Teams met in two occasionsProgress Meeting 10-12 Sept 2007 hosted at Institute of Geography (Baku, Azerbaijan)Final Meeting 24-26 Sept 2008 held at Castiglioncello (Livorno, Italy)

Project supported exchange visits of team members to cooperate on specific topics, e.g.:

White and Barents seas (NOCS & GC) –Development of a new local tidal correctionCaspian Sea (CNR & LEGOS & IG) –Validation of the altimetric products

ALTICORE - running


Concerns:Where are data located? In what quantity? Of what quality?Who owns data? How to access?

What we have seen:Different samplingManual recordingOften gappy or collection stoppedJust tables (no metadata)Language differences

Jiloy, Zhiloy, Chilov – same station!!!

Caspian Sea – in situ sea level infrastructure

BUT ….the quality and usability of the altimeter-derived observations is dependent upon good calibration/validation

of the satellite sensors with in situ observations.

Source:Caspian Env Programme

1999

Notsurprised !!!

We liaised with scientists, whoplay with numbers.They are not data producers!


Caspian Sea – Water level variability from in situ data

Longest record at Baku (since 1837)Shows a rising of more than 2 metres between 1977 and 1995Now stabilized near the −27 m levelUnderstanding variability at all scales – a complicated puzzleCombination of factors: climatic (atmospheric variations), anthropogenic (e.g. river drainage and water use, especially Volga), geologic (e.g. subsidence)The question - Will the Caspian sea level rise again ?

Baku


Caspian Sea – Comparison at different stations Makhachkala - Krasnovodsk

-0.2-0.1

00.10.20.30.40.50.60.7

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994

Date (year)

diffe

renc

e (m

)

Makhachkala - Ogurchinsky

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00.10.20.30.40.50.60.7

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994

date (year)di

ffere

nce

(m)

Makhachkala-Kulaly

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00.10.20.30.40.50.60.7

1976 1978 1980 1982 1984 1986 1988 1990 1992 1994

Date (year)

diffe

renc

e (m

)

Makhachkala

OgurchinskyIsland

Kulaly Island

Assumed Makhachkala as referenceGood agreement with observations at Krasnvodsk and OgurchinskySome discrepances at Kulaly island

To be noted: The Northern Caspian presents peculiar metocean dynamics with strong storm surges over shallow waters (averaging just 4 meters)

Krasnovodsk


Caspian Sea – Multi-Mission Altimetry Ground Track Coverage

Fixed issues:Radar Altimeter – land contamination of footprint (0-10 km)Wet Tropo correction (radiometer) – land contamination of footprint (0-50 km)Dry and Wet Tropo corrections (from ECMWF/NCEP fields) – erroneous altitude in the algorithm (e.g. T/P) Mean Sea Surface (CLS01) not usable to compute SLAsAliasing of high-frequency variability (weather) - mis-modeled or un-modeled

Varying features (Northern Caspian):Uncertainties in the retrieval (surge or spike)Sea waters frozen for around 4-5 months (from November to March)

Unknown features:Land/sea transition (high res DEM and Bathymetry)


42°

43°

44°

45°

46°

47°

Nor

th la

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e

46° 48° 50° 52° 54° 56°East longitude

p92

Tyuleniy Is.

Chistaya Banka Is.

Backscatter Coefficient

Black dots – Ice Edges from AMSR-E/Aqua data

(available since 2004)

Jason-1 pass 92

Wet Troposphere from satellite radiometer

White band - Island effects ?

Chistaya Banka Island

Caspian Sea – Ice in altimeter and radiometer footprints


-28.

5-2

8-2

7.5

-27

-26.

5-2

6Se

a le

vel (

m)

1986 1988 1990 1992 1994 1996 1998 2000Time (year)

CSR95

OSU95

GSFC00

CLS_SHOM98

CLS01

MSS Model:

Starting computing local MSS(GCRAS06)

Where & Why ?Time intervals used to construct different MSS

Sea Level Anomaly computed from standard MSS is goodfor deep basins but not for shelves and slopes

Caspian Sea – Mean Sea Surface (MSS)


Based on 1 Hz dataReferred to Baltic Sea level reference frameShows seasonal variations probably due to climatological (evaporation & precipitation) and hydrological (river runoff, discharge to Kara Bogaz Gol) cycle Inter-annual tendencies might be interpreted in the light of decadal climate variability and amplification of irrigation in the Volga river basin

Caspian Sea – Water level variability from multi-mission altimetry


Agree well with “ground truth” at basin scale, but still some local « mysteries » (e.g. 70 mm in 1995)Errors in altimetry ~15 mm/yrPossible uncertainty in the global lake level deduced from in situ stations

Need of a permanent Cal/Val site for satellite altimetry

-27,2-27,1

-27-26,9-26,8-26,7-26,6-26,5

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Time (year)

Sea

leve

l (m

)Caspian Sea – Comparison of TOPEX/Poseidon altimetry (red) and in situ stations (black)

?


Sea level pilot station operating at Absheron Port (Baku)

Satellite altimetry ground tracks Jason (red), Envisat (white), GFO (green), T/P 2002-2005 (yellow)


Started to collect data in June 2008 and still ongoingProcessed the first 8 monthsWork in progress …..

Some pictures about field work in June 2008


During the observational period, the sea level at Port Absheron exhibits a large high frequency variability apparently more pronounced during summer timeThere are also other oscillations superimposed that need careful investigation

Sea level variability at Absheron Port

The spectrum analysis shows the existence of a little tidal contribution to the sea levelThe large contribution is observed in the 3-30 day band, possibly linked to the meteorological forcing


New EU/FP7 Coordination Action CASPINFO - (started on Sep 2008)Fostering improved co-operation between research institutes, oil & gas industries, and international bodies in the Caspian SeaMARIS (Netherlands) is the coordinatorBrings together partners from riparian countries (Russia, Azerbaijan and Kazakhstan) + EU ( Greece, Italy) + IOC-IODE, CEP and BSCS More at www.caspinfo.net

Raising funding (jointly with LEGOS)to make the pilot station GLOSS-compliant, including near real time transmission, permanent GPS Station to control the vertical motion of the sea level sensor and regular offshore leveling along the altimetry ground tracksRecommendation to ESA for Sentinel-3

Caspian Sea - Beyond ALTICORE

Caspian Sea is currently the best natural target for calibration over continental water bodies being a big lake with favorable location of

satellite tracks and cross-over pointsCaspian Sea be used as testbed for developing a cal/val site for lakes. No similar optimality of any existing cal/val site in Europe would satisfy these requirements.

http://www.caspinfo.net/


Sea level in the Caspian SeaTopic of growing concern to all five surrounding countries (Azerbaijan, Republic of Iran, Kazakhstan, Russian Federation and Turkmenistan) Several low-lying and densed-populated coastal areas

Satellite altimetry in the Caspian SeaConceptually simple, but challenged by specific processing Measuring sea level changes beyond political barriers

In situ sea level measurements in the Caspian SeaCritical for the generation of accurate altimeter-derived estimatesNot only “numbers” but also knowing how they were generated

Additional in situ resources in the Caspian SeaKey role to support analysis of the various met-ocean-hydro contributionsOil & Gas sector interested - it would be an important player

Data are only one piece of the puzzleWe know the sea level storyWe don’t know “What-if”

Summary

Remote Sensing in the Caspian Sea would be an important factor of integration and a valuable opportunity for data sharing

satellite radar altimetry for monitoring caspian sea level changes

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