QWG8, Boutin et al. SMOS and Aquarius: SSS and Wind Effect J. Boutin, X. Yin, N. Martin (LOCEAN, Paris), E. Dinnat (Chapman University/NASA/GSFC), S. Yueh (NASA/JPL) Coll. G. Reverdin (LOCEAN), G. Alory (LEGOS), F. Gaillard (LPO) ESA Expert Support Lab.(ARGANS, ICM, Ifremer, ACRI-st, CLS) ESA/CNES SMOS CAL/VAL project (GLOSCAL) NASA ROSES project (Intercalibration of SMOS and Aquarius)
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QWG8, Boutin et al. SMOS and Aquarius: SSS and Wind Effect J. Boutin, X. Yin, N. Martin (LOCEAN, Paris), E. Dinnat (Chapman University/NASA/GSFC), S. Yueh.
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QWG8, Boutin et al.
SMOS and Aquarius: SSS and Wind Effect
J. Boutin, X. Yin, N. Martin (LOCEAN, Paris),
E. Dinnat (Chapman University/NASA/GSFC),
S. Yueh (NASA/JPL)
Coll. G. Reverdin (LOCEAN), G. Alory (LEGOS), F. Gaillard (LPO)
ESA Expert Support Lab.(ARGANS, ICM, Ifremer, ACRI-st, CLS)
ESA/CNES SMOS CAL/VAL project (GLOSCAL)
NASA ROSES project (Intercalibration of SMOS and Aquarius)
QWG8, Boutin et al.
Overview of this presentation
• SMOS – Aquarius – ARGO maps
• SMOS & Aquarius wind dependencies
• Comparisons of SMOS SSS wrt in situ measurements (ship and ARGO)
• Influence of using SSMI WS intead of ECMWF
QWG8, Boutin et al.
Data
Improvements with respect to previous versions:
-Reduced coastal bias; OTT (systematic bias in the Field of View) every 2 weeks and
separetely for ascending and descending orbits; improved wind correction ; improved
RFI & outlier sorting
SSS averages weighted by the variance of the error of the retrieved SSS
(Boutin et al., TGRS, 2012), and restricted to wind speed between 3 and
12m/s
USE ONLY ASCENDING ORBITS
SATELLITE SSS-SMOS SSS reprocessed by ESA v5.5 (wind-model 1)
-AQUARIUS level 3 maps v1.2.3
IN SITU SSS
-Optimal Interpolation of ARGO SSS: IFREMER In Situ Analysis System (ISAS)
(Gaillard et al. 2009)
-ARGO SSS (upper SSS between 10m and 0.5m depth) (CORIOLIS GDAAC)
-Ships of Opportunity (Delayed mode data delivered by SSS observatory
(http://www.legos.obs-mip.fr/observations/sss/))
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Ascending vs Descending SSS: Sept 2011
SSS Ascending orbits SSS Descending orbits
SSS error Ascending orbits SSS error Descending orbitsDescending OTTs not enough to remove stripesespecially in September=> Sun alias? Galactic noise?
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Sept-Dec 2011
SMOS v5.5(Ascending Orbits)
Aquarius v1.2.3
ARGO OI
SMOS - AQUARIUS – ARGO SSS – Sept-Dec 2011
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SMOS-Aquarius
SMOS-ARGO OI
Aquarius-ARGO OI
Sept-Dec 2011
SMOS features: -issues close to land (image reconstruction) -Large RFI (N. Atl., Asian coasts) -Ice edge
Aquarius features: -Underestimates in Southern Ocean -Overestimates close to islands (e.g. S. Pac ).
SMOS & Aquarius features: -Better resolution of Amazone Plume -Lower SSS in rainy regions -Lower SSS in Indian Ocean
-1 +1
-1 +1
-1 +1
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SMOS & AQUARIUS WIND DEPENDENCIES
Aquarius Tb-wind :
-empirical wrt SSMI wind speed + NCEP wind direction (Yueh)
-Empirical model wrt ECMWF wind speed (Tenerelli, 2011)
-Empirical model wrt ECMWF wind speed (Guimbard et al, 2012)
Given the uncertainty about the absolute bias between model and data (need for OTT
correction for SMOS) all the curves have been adjusted at 7m/s
QWG8, Boutin et al.
Very similar SMOS and Aquarius Tb-Wind omnidirectional dependencies 3<WS<12 m/sAbove 15m/s SMOS T higher than Aquarius T (especially in H polarization)
Mean and std of difference (SMOS-Ship SSS) over the whole period 2010-2011and July-Aug-Sept
Coast/RFIBiases?
Std ~0.2-0.3 (except north of 25N in winter-Spring; RFIs?)
(all sections except 19-Oct-2010, 11-Jul-2010 et 14-Mar-2011 )
10N 15N 20N Latitude 30N 35N
-0.2
0.2
1
-1
Bia
s an
d st
d(di
ff)
Black /grey: all monthsColors: July-Aug-Sept
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RFI sorting needs to be improved!!
35.5
38.5
16N 34N
June 2011
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Conclusion
SMOS SSS:• In tropical-subtropical regions, far from land, in non rainy region, precision
at 100x100km2-10days ~0.3
• SMOS SSS freshening wrt in situ SSS (~5m depth) in rainy conditions: true salinity effect? Needs for surface drifters for validation (needs for a lot of matchups!!!)
• Ship TSG: very useful for validating ‘small scale’ (<200km) variability (gradients) seen by SMOS
• Still issues (sun aliases, land vicinity, ice edge, RFI sorting …): image reconstruction still in progress
SMOS and Aquarius wind models
• Tb-wind SMOS and Aquarius very similar: 3-12m/s but Aquarius lower above 12m/s; Aquarius azimuth dependency much larger at high wind speed
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Issues about wind speed uncertainties and SMOS retrieved SSS
Yin X.1, Boutin J.1, Martin N.1, Vergely J.2, Spurgeon P.3
1. LOCEAN/IPSL, UMR CNRS/UPMC/IRD/MNHN, France 2. ACRI-ST, France 3. ARGANS, United Kingdom
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OutlineImpact of wind speed uncertainties on SMOS retrieved SSS
1) SSMI versus ECMWF wind speed
2) Difference in retrieved SSS using two different prior wind speeds
3) The eastern equatorial Pacific Ocean
Conclusions and perspectives
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Wind speed retrieved from SMOS data
August 2010, ECWMF wind speed used as prior.
-300 300
WS (retrieved-prior)
Distance to the track (km)
Latitude
40N
50S
Incidence angle
60
0
Eta
Distance to the track (km)
In the centered swath (within +-300km), wind speed is adjusted with SMOS data; in the border of the swath (outside of +-300km), wind speed can not be adjusted with SMOS data (not enough incidence angles).
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Data
1. SMOS Brightness temperature (last reprocessing: L1c v504)1) August 2010, 436 ascending orbits over global ocean2) September 2011, 418 ascending orbits over global ocean
2. ECMWF wind speed collocated with SSMI wind speed,August 2010 and September 2011collocation radii of ±0.5 hour and ±50 km
3. SSS1) SMOS SSS retrieved with ECWMF wind as prior. Roughness model fitted from ECMWF wind speed (Yin et al., TGRS SMOS special issue, 2012) is used. ( ESA reprocessing v550)
2) SMOS SSS retrieved with SSMI wind as prior, processed by LOCEAN. Roughness model fitted from SSMI wind speed (Yin et al., TGRS SMOS special issue, 2012) is used.
3) ARGO optimal interpolation (ISAS) (Gaillard et al. 2009) used as reference
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For the orbit 20100809T142544_20100809T151945, the ECMWF and SSMI wind speeds are quite different around 17S.
One example of differences between ECMWF, SSMI and retrieved WS from SMOS data
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Latitude
TB simulations with SSMI Wind
5 points running mean of SMOS TB
TB simulations with ECMWF Wind
No matter whether SSMI or ECWMF wind is used as prior, retrieved wind speed is closer to SSMI wind speed but still a little bit lower.
TB simulations with SSMI Wind are closer to SMOS TB
August 2010 monthly averageSMOS SSS (+-300km)3-12m/s (both ECWMF and SSMI)
Similar spatial distribution
The same for September 2011, not shown here.
SMOS SSS with SSMI wind speed
SMOS SSS with ECMWF wind speed
ARGO OI SSS
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August 2010 monthly averageSMOS SSS – ISAS/ARGO SSS3-12m/s
1. In the eastern equatorial Pacific ocean, differences between SMOS SSS with SSMI WS and ARGO OI SSS are often lower than those with ECMWF WS.
2. In the eastern part of Pacific and Atlantic ocean, SSMI WS are lower than ECMWF WS. Also, the retrieved SSS with SSMI WS are lower than those with ECMWF WS.
Similar patterns in September 2011, not shown here.
SMOS– ARGO OI SSS, SSMI prior wind speed
SMOS– ARGO OI SSS, ECMWF prior wind speed
1
-1
1
-11
-11
-1
SMOS SSS (SSMI) – SMOS SSS (ECMWF)
WS (SSMI) – WS (ECMWF)
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Retrieved WS(ECMWF)
Retrieved WS(SSMI)
rWS(ECMWF)- ECMWF WSrWS(SSMI)- SSMI WS
-Monthly averaged August 2010-
1. In the eastern equatorial Pacific ocean, SSMI WS are much lower than ECMWF WS. 2. Retrieved WS with ECMWF WS are trying to get close to SSMI WS but not close enough.
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Conclusions and Perspectives
1. In the centered part of the swath (within +-300km), wind speed is adjusted with SMOS data; In the border of the swath (outside of +-300km), wind speed can not be adjusted with SMOS data.
2. In the centered part of the swath (+-300km), the difference between SMOS SSS and ARGO OI SSS is lower than the border, since wind speed is corrected (partly) with SMOS data.
3. Locally (eastern equatorial Pacific), SSMI wind speeds used as prior in the retrieval perform better (SMOS retrieval scheme not able to completely correct for the differences between SSMI and ECMWF WS, but it decreases SSS bias locally).
4. Origin of differences in eastern equatorial Pacific?
5. Work in progress….
QWG8, Yin et al.
Sensitivity of L-band Tb (h- & v-pol) to θ, wind speed and SSS
Incidence angle
Incidence angle
From Dinnat et al. 2003
Incidence angle (°)
Tv/ WS >0 and with incidence angle
Tv/ SSS<0 and abs() with incidence angle
Th/ WS>0 and with incidence angle
Th/ SSS<0 and abs() with incidence angle
(at nadir, 20°C, Tb/ WS ~0.2K/m/s, Tb/ SSS~-0.5K/psu => a bias of 5m/s on WS ~ a bias of -2psu on SSS)
SMOS SSS (ESA level 2 retrieval) is retrieved through a least square minimisation of the difference between SMOS and modeled Tb.
1
02
2,
1
02
2mod2 ),( Np
j P
priorjjNm
i T
bimeas
ib
jib
PPPTT
Retrieval of SSS (=100psu), SST (=1°C), WS(=1.5m/s on wind components) through the minimisation of:
=> estimate of SSS error (Levenberg & Marquard algorithm)
SMOS SSS and WS retrieval method
QWG8, Yin et al.
SSS v5 Descending August & September 2010 & 2011
August 2010
September 2011August 2011
September2010
Descending OTTs not enough to remove stripesLarger stripes in September than in August=> Sun alias? Galactic noise?
Less outliers in the northern Atlantic in 2011 than in 2010Decrease of RFIs