validation over the northwestern mediterranean sea (map team) jérôme bouffard y. ménard, l....
TRANSCRIPT
Validation over the Northwestern Mediterranean
Sea (MAP team)
Jérôme BouffardJérôme Bouffard
Y. Ménard, L. Roblou, F. Birol, F. Lyard, R. MorrowY. Ménard, L. Roblou, F. Birol, F. Lyard, R. Morrow
Improved Satellite Improved Satellite Altimeter data dedicated Altimeter data dedicated
to coastal areas :to coastal areas :
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ContextContext
Western Mediterranean Sea
Longitude
Latitudes
Gulf of Genoa
Altimetric tracks: - Topex/poseidon- Envisat- jason 1- GFOTide gauges:
LPCLPCCurrentCurrent
Corsica Channel
Gulf of Lion
Catalan Sea
Ligurian Sea
Balear islands
Algerian Bassin
Liguro Provencal Catalan (LPC) currentLiguro Provencal Catalan (LPC) currentComplex small mesoscale dynamics (Send, 1999)
LPC Instability + meanders (Conan and Millot, 1995) Seasonnal variability (Millot 1991)
Are altimeter data valuable in coastal areas ?Are altimeter data valuable in coastal areas ?How to improve altimeter data in coastal areas?How to improve altimeter data in coastal areas?
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Available dataAvailable data
Features:• Standard editing• MOG2D Global (w+P) + FES2004 (tide) corrections• Along-track sampling every 7km (~ 1HZ)• Large scale and orbit error reduction (Le Traon et Ogor,
1998)
Standard distributed data:Standard distributed data:
AVISO regional along-track product: DT-(M)SLA “Upd”
Improved coastal data:Improved coastal data:Margins Altimetry Projects (MAP) : Xtrack SLA (see Lyard et al OSTST 2007)
Features:• Specific editing and correction re-building• MOG2D -Medsea (w+P) + MOG2D-Medsea (tide)
corrections• High resolution sampling every 350 or 700 m (~ 10HZ/
20 HZ)
Example at the Nice TGExample at the Nice TG
Impact of the processing Impact of the processing featuresfeatures
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Comparisons at the Nice TG:% of RMS explained: Impact of Impact of regional de-aliasingregional de-aliasing
correctionscorrectionsCorrelation: 0.75Residual RMS: 4.1 cmRMS explained: 33%
NiceTG
MAP-Xtrack GlobalGlobal de-aliasingGlobal de-aliasing
Correlation: 0.78Residual RMS: 3.9 cmRMS explained: 37%
MAP-Xtrack Medsea
Regional de-aliasingRegional de-aliasing
NiceTG
%10 40
MOG2D Medsea (Regional configuration) significantly improves the consistency beween the altimeter and the Nice tide gauge time series.
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Correlation: 0.78Residual RMS: 3.9 cmRMS explained: 36%
MAP-xtrack MedseaHF no editing
NiceTG
Standard editingStandard editing
Correlation: 0.81Residual RMS: 3.7 cmRMS explained: 40%
NiceTG
MAP-Xtrack Medsea HF
Specific editingSpecific editing
%10 40
Comparisons at the Nice TG:% of RMS explained: Impact of the Impact of the datadata editing methodologyediting methodology
The specific data editing methodology allows to decrease the noise in the altimeter time series
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Correlation: 0.78Residual RMS: 3.9 cmRMS explained: 37%
MAP-Xtrack Medsea
1HZ sampling1HZ sampling
NiceTG
Correlation: 0.81Residual RMS: 3.7 cmRMS explained: 40%
NiceTG
MAP-Xtrack Medsea HF
HF samplingHF sampling
%10 40
Comparisons at the Nice TG:% of RMS explained: Impact of the Impact of the High Frequency samplingHigh Frequency sampling
The high frequency sampling allows to go closer to the coast
Example at the Nice Tide GaugeExample at the Nice Tide Gauge
Comparisons of the Map-Comparisons of the Map-Xtrack data with a regional Xtrack data with a regional
standard productstandard product
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The MAP-Xtrack processing allows to recover more data far more data far and close to the coastand close to the coast
Comparisons at the Nice TG:Number of dataNumber of data MAP-Xtrack Medsea HFMAP-Xtrack Medsea HF vsvs DT-(M)SLA UpdDT-(M)SLA Upd
NiceTG
MAP-Xtrack Medsea HF
NiceTG
DT-(M) SLA Upd
AVISOproduct
MAPproduct
115 125 115 125
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NiceTG
NiceTG
• Better statistical results for the the Xtrack-HF dataBetter statistical results for the the Xtrack-HF data
Comparisons at the Nice TG:% of RMS explained:% of RMS explained: MAP-Xtrack Medsea HFMAP-Xtrack Medsea HF vsvs DT-(M) SLA UpdDT-(M) SLA Upd
MAP-Xtrack Medsea HF
DT-(M) SLA Upd
Correlation: 0.74% of RMS explained: 32.9
Correlation: 0.79% of RMS explained: 38.4
Correlation: 0.79% of RMS explained: 36.5
Correlation: 0.81% of RMS explained: 40.4
Detection of small coastal spatial structure: are they physically reallistic ?Are they Linked with the LPC dynamics ?
LPC
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2
AVISOproduct
MAPproduct
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Hovmuller plots of across track geostrophic Hovmuller plots of across track geostrophic velocity anomalies (TP track-222 in 2001)velocity anomalies (TP track-222 in 2001)
latitude
Tim
e
Aviso product MAP product
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LPC current LPC current Close to the LPC and to Close to the LPC and to the coast:the coast: The two signals are well The two signals are well phased:phased:
The altimetric signal has The altimetric signal has a lower amplitude:a lower amplitude:Intrinsic seasonal variability of the LPC is shifted toward the steric signal.
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Tim
e
Eddy ?Eddy ?Meander ?Meander ?A
ugust
Janu
ary
Far from the LPC:Far from the LPC:Dephasing between the Dephasing between the two signals:two signals: the Offshore and the coastal don’t « see » the same dynamics (eddy ?) .The altimetric and TG The altimetric and TG signals have equivalent signals have equivalent amplitude:amplitude: The steric effect is a large wavelenght signal
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August January
2
Coastoffshore
cm/s
Example at the Sete Tide GaugeExample at the Sete Tide Gauge
Comparisons of the Map-Comparisons of the Map-Xtrack data with a regional Xtrack data with a regional
standard productstandard product
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Comparisons at the Sète TG:Number of available dataNumber of available data MAP-Xtrack Medsea HF vs DT-(M)
Upd
MAP-Xtrack medsea HF processing allows to recover more data far and close to the coastmore data far and close to the coast
MAP-Xtrack Medsea HF DT-(M) SLA Upd
MAPproduct
Avisoproduct
95 120 95 120
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Comparisons at the Sète TG:% of RMS explained:% of RMS explained: MAP-Xtrack Medsea HF vs DT-(M) SLA Upd
Correlation: 0.89% of rms explained: 52.8
Correlation: 0.79% of rms explained: 38.9
Correlation: 0.84% of rms explained: 45.6
Correlation: 0.77% of rms explained: 35.9Sète TG Sète TG
DT-(M) SLA UpdMAP-Xtrack Medsea
HF
Better statistical results for the the Xtrack-HF dataStronger improvement than at Nice TG
MAPproduct
Avisoproduct
10 40 10 40% %
Mean statistics at Tide gauges Mean statistics at Tide gauges over the whole areaover the whole area
Comparisons of the Map-Comparisons of the Map-Xtrack data with a regional Xtrack data with a regional
standard productstandard product
Tide Gauges
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DT-(M) SLA 90 73 0.77 4.4 34 %
Xtrack 99 61 0.83 3.7 44 %
Number of dataNumber of dataDistance to Distance to TGs (km)TGs (km)
CorrelationCorrelation RMS differenceRMS difference(cm)(cm)
% of RMS% of RMS explainedexplained
MAP
Multi-satellite: Mean Statistics at TGsMulti-satellite: Mean Statistics at TGsTopex / PoseidonTopex / Poseidon
Xtrack
Std. editing39 50 0.82 3.9 43 %
DT-(M) SLA 39 60 0.75 4.8 34 %
GFOGFO
DT-(M) SLA 38 69 0.80 4.2 36 %
Jason 1Jason 1
Xtrack
Std. editing
+ orbit adjust.
39 59 0.81 3.9 39 %
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• Processings– Specific editings allow to eliminate spurious data and improve the
quality of coastal altimetric products – Regional de-aliasing models strongly improves altimetric data – High frequency along track sampling allow to highlight small spatial
dynamical processes
• Comparisons with a standard product– More coastal data with the MAP processings – Closer to the coastline – Better quality of the altimetric data
• Applications– Validation of Regional 3D models
– Cal/Val– Monitoring of transport in marginal areas
ConclusionConclusionSea level anomalies comparisons in the Bay of Biscay along Jason-1 ground track 137 (July-August 2004).
Blue: altimeter data
Red: Symphonie coastal model
• Good agreements on instantaneous sea levels
• Satisfying correlation for synoptic scales and meso-scales dynamics
• Altimeter data exhibit short scales processes not represented in the model simulations
See also Roblou et al, « x-track a new processing tool for altimetry in coastal oceans »
Correlation SYMPHONIE model elevations – altimetry SLA: TOPEX + GFO
Sea level anomalies comparisons in the Mediterranean Sea along Multi-satellite ground track (2001-2003).
See also Bouffard et al, « Improved Altimetry in the Northwestern Mediterranean : Comparison of Ocean Dynamics with a Regional Circulation Model »
Correlation SYMPHONIE model elevations – altimetry SLA: Jason + GFO
Correlation SYMPHONIE model elevations – altimetry SLA: Jason + GFO + Envisat
2001
2002
2003
0.7 0.9
0
0,02
0,04
0,06
0,08
0,1
0,12
0,14
0,16
0,18
0 20 40 60 80 100 120 140 160
Cycle
SSH
abs
olut
e bi
as (m
)
SSH absolute bias at M3 tide gauge, Jason-1 pass 085
Mean=0.1046m
Std dev=0,0252m
Jason-1 pass 222
Jason-1 pass 085
M3 tide gauge (Senetosa)
CAL/VAL at the Senetosa Tide Gauge
CrossoverEnvisat 257
Jason85
CrossoverEnvisat 258
Jason44
CrossoverEnvisat 588 Envisat 257
CrossoverEnvisat 588
GFO 257
CrossoverEnvisat 588
Jason 44
CrossoverGFO 257Jason 85
CrossoverJason 44Jason 85
Crossover pointsCrossover points
Merid
ion
al dirrectio
n
Ligurian Sea
Corsica C
hannel
In-situstation
Comparisons with the normalized transport (from in-situ data)
Multi-satellite crossover geostrophic velocities
Ellipses of geostrophic velocity anomalies at altimetric crossovers
See also poster Bouffard et al, «A view from multi-mission satelite altimetry over the coastal ocean: a study in the Ligurian Sea and the Corsica channel. » (OSTST 2007)