vignudelli: altimetric observations in the caspian sea

Satellite radar altimetry for monitoring Caspian
sea level changes
Lessons learned from the
EU/INTAS ALTICORE project
Presented by
Stefano Vignudelli
Consiglio Nazionale delle Ricerche, Italy
Contributors:
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)
Satellite
ALTImetry
for
COastal REgions
NATO ARW Ferrara December 2-4
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Outline of my talk
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Satellite Altimetry in few words
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ALTICORE Project in a nutshell
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Who, what, where, how
Lesson learned in the Caspian Sea
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Open ocean
Coastal zone
Challenges with sea level data
Some examples
Preliminary results from a pilot sea level station
Beyond ALTICORE
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Initiatives
Summary – a personal view
NATO ARW Ferrara December 2-4
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How does satellite altimetry work ?
What are we measuring?
Satellite
The Altimeter is
nadir-poiting radar
Not Images but points
along a track!
S
Orbit
R = ½ ct
Radar Return Signal
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η
SSH
Reference
Ellipsoid
G
Geoid
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Open Ocean
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)
Satellite altimetry is success story
in open ocean and next step is …
NATO ARW Ferrara December 2-4
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Meeting challenges in other areas
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Coastal Zone, Inland Seas, Rivers,
Sea Ice Areas
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17 yrs multi-mission archive
Not fully exploited
Normally flagged as bad in the official
products
Coastal Zone
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Common technical issues
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There is much interest in bring
altimetry to the coastline
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Contamination of radar footprints
Inadequacy of even failure of some
auxiliary corrections
Re-thinking the quality control strategy
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A hope at horizon: progresses in
technology promise better
resolution capability
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Source: COASTALT
Envisat data
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.
New techniques (Delay-Doppler,
Interferometry, Reflectometry)
New concepts (Constellations)
A good thing is that future sensors
(AltiKa, WSOA, SIRAL on Cryosat,
Sentinel-3 altimeter…) are being
designed with an eye to coastal zone
NATO ARW Ferrara December 2-4
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Coastal Altimetry – a bit of story
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Some seminal papers
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Crout 1998 - could recover data when coastal topography is flat
Anzenhofer et al. 1999 – retracking waveforms
Vignudelli et al. 2000 - Signal recovered consistent with in situ data
Started first program in 2001
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ALBICOCCA - ALtimeter-Based Investigations in COrsica, Capraia and Contiguous Area
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Precursor of other projects
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ALTICORE (2007-2008)
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to replicate in Caspian, Black, White, Barents, India and Africa
Focus on Envisat mission at 18 Hz (350 m)
NW Med, Iberian and West Britain are the pilot sites
PISTACH (2007-2008)
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More here today
COASTALT (2008 – now)
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Focus on Jason mission
Global coasts & inland waters
NASA OST ST call (2008-now)
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NW Mediterranean proposed as the “operational lab” for coastal altimetry
Backward reanalysis of standard products (1HZ i.e. 7 km)
A revised post-processing strategy
3 projects on “Coastal Ocean” and other three ones coastal-related
… & at centre of the community
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Regular workshops
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Silver Spring 2007, Pisa 2008, Frascati 2009, suggested Porto 2009) – see at www.coastalt.eu
Springer Book
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20 chapters, 70 people involved – see at www.alticore.eu/book
One of the chapters is about Caspian Sea
NATO ARW Ferrara December 2-4
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ALTICORE - Cooperation
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Funded by EU under INTAS Program
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Coordinating partner:
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providing altimeter data – more, better, closer coasts
enhancing the capacity of Eastern partners to exploit data
This is done in a number of regional seas
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P. P. Shirshov Institute of Oceanology (Russia)
Geophysical Center (Russia)
Institute of Geography (Azerbaijan)
Aiming at
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National Oceanography Centre Southampton (UK)
Laboratoire d'Etudes en Géophysique et Océanographie Spatiales (France)
Three Eastern partners took part:
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Consiglio Nazionale delle Ricerche (Italy)
EU partners involved:
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Started on December 2006 for for a period of two years
Mediterranean, Black, Caspian, White, Barents
Three priority topics for action in the Caspian Sea:
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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
NATO ARW Ferrara December 2-4
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ALTICORE - running
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Teams met in two occasions
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Progress 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.:
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White and Barents seas (NOCS & GC) –
Development of a new local tidal correction
Caspian Sea (CNR & LEGOS & IG) –
Validation of the altimetric products
NATO ARW Ferrara December 2-4
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Caspian Sea – in situ sea level
infrastructure
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Concerns:
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Source:
Caspian Env
Programme
1999
Where are data located?
In what quantity?
Of what quality?
Who owns data?
How to access?
What we have seen:
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Different sampling
Manual recording
Often gappy or collection stopped
Just tables (no metadata)
Language differences
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Not
surprised !!!
Jiloy, Zhiloy, Chilov – same station!!!
We liaised with scientists, who
play with numbers.
They are not data producers!
BUT ….the quality and usability of the altimeter-derived
observations is dependent upon good calibration/validation
of the satellite sensors with in situ observations.
NATO ARW Ferrara December 2-4
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Caspian Sea – Water level variability
from in situ data
Baku
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Longest record at Baku (since 1837)
Shows a rising of more than 2 metres between 1977 and 1995
Now stabilized near the −27 m level
Understanding variability at all scales – a complicated puzzle
Combination 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 ?
NATO ARW Ferrara December 2-4
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Caspian Sea – Comparison at
different stations
Makhachkala - Krasnovodsk
difference (m)
Kulaly Island
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
Makhachkala
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
Date (year)
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Assumed Makhachkala as reference
Good agreement with observations
at Krasnvodsk and Ogurchinsky
Some discrepances at Kulaly island
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To be noted: The Northern Caspian
presents peculiar metocean
dynamics with strong storm surges
over shallow waters (averaging
just 4 meters)
difference (m)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
date (year)
Makhachkala-Kulaly
difference (m)
Krasnovodsk
Ogurchinsky
Island
Makhachkala - Ogurchinsky
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
1976
1978
1980
NATO ARW Ferrara December 2-4
1982
1984
1986
1988
1990
1992
1994
Date (year)
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Caspian Sea – Multi-Mission
Altimetry Ground Track Coverage
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Fixed issues:
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Varying features (Northern Caspian):
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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 SLAs
Aliasing of high-frequency variability
(weather) - mis-modeled or un-modeled
Uncertainties in the retrieval (surge or
spike)
Sea waters frozen for around 4-5 months
(from November to March)
Unknown features:
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Land/sea transition (high res DEM and
Bathymetry)
NATO ARW Ferrara December 2-4
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Caspian Sea – Ice in altimeter and
radiometer footprints
Wet Troposphere from satellite radiometer
47°
46°
North latitude
Chistaya
Banka
Is.
Chistaya
Banka
Island
45°
Tyuleniy Is.
2
p9
44°
43°
42°
46°
48°
50°
52°
54°
Jason-1 pass 92
Backscatter Coefficient
East longitude
56°
White band - Island effects ?
Black dots – Ice Edges
from AMSR-E/Aqua data
(available since 2004)
NATO ARW Ferrara December 2-4
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Caspian Sea – Mean Sea Surface (MSS)
Sea Level Anomaly computed from standard MSS is good
for deep basins but not for shelves and slopes
Time intervals used to construct different MSS
-26
Where & Why ?
-27
-27.5
-28.5
-28
Sea level (m)
-26.5
MSS Model:
CSR95
OSU95
GSFC00
CLS_SHOM98
CLS01
1986
1988
1990
1992
1994
Time (year)
1996
1998
2000
Starting computing local MSS
(GCRAS06)
NATO ARW Ferrara December 2-4
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Caspian Sea – Water level variability from
multi-mission altimetry
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Based on 1 Hz data
Referred to Baltic Sea level reference frame
Shows 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
NATO ARW Ferrara December 2-4
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Sea level (m)
Caspian Sea – Comparison of TOPEX/Poseidon
altimetry (red) and in situ stations (black)
?
-26,5
-26,6
-26,7
-26,8
-26,9
-27
-27,1
-27,2
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Time (year)
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Agree well with “ground truth” at basin scale, but still some
local « mysteries » (e.g. 70 mm in 1995)
Errors in altimetry ~15 mm/yr
Possible uncertainty in the global lake level deduced from
in situ stations
Need of a permanent Cal/Val site for satellite altimetry
NATO ARW Ferrara December 2-4
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Sea level pilot station operating
at Absheron Port (Baku)
Satellite altimetry ground tracks
Jason (red), Envisat (white), GFO
(green), T/P 2002-2005 (yellow)
NATO ARW Ferrara December 2-4
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Some pictures about field work in
June 2008
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Started to collect data in June 2008 and still ongoing
Processed the first 8 months
Work in progress …..
NATO ARW Ferrara December 2-4
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Sea level variability at Absheron Port
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During the observational
period, the sea level at
Port Absheron exhibits a
large high frequency
variability apparently
more pronounced during
summer time
There are also other
oscillations superimposed
that need careful
investigation
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The spectrum analysis
shows the existence of a
little tidal contribution to
the sea level
The large contribution is
observed in the 3-30 day
band, possibly linked to
the meteorological forcing
NATO ARW Ferrara December 2-4
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Caspian Sea - Beyond ALTICORE
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New EU/FP7 Coordination Action CASPINFO - (started on Sep 2008)
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Fostering improved co-operation between research institutes, oil & gas
industries, and international bodies in the Caspian Sea
MARIS (Netherlands) is the coordinator
Brings 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)
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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
tracks
Recommendation to ESA for Sentinel-3
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 points
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Caspian 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.
NATO ARW Ferrara December 2-4
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Summary
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Sea level in the Caspian Sea
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Satellite altimetry in the Caspian Sea
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Critical for the generation of accurate altimeter-derived estimates
Not only “numbers” but also knowing how they were generated
Additional in situ resources in the Caspian Sea
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Conceptually simple, but challenged by specific processing
Measuring sea level changes beyond political barriers
In situ sea level measurements in the Caspian Sea
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Topic 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
Key role to support analysis of the various met-ocean-hydro contributions
Oil & Gas sector interested - it would be an important player
Data are only one piece of the puzzle
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We know the sea level story
We don’t know “What-if”
Remote Sensing in the Caspian Sea would be an important
factor of integration and a valuable opportunity for data sharing
NATO ARW Ferrara December 2-4
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