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lfre
mer
Atelier Moment Cinetique Paris 26 Novembre
2012
Les Vents de Surface Diffusiométriques
1992
2020
92 94 96 98 00 02 04 06 08 10 12 14 16 18 20
ERS-1
ERS-2
ADEOS-1
QuikSCAT
ADEOS-2
MetopA
OSCAT2
HY-2A
MetopB
CFOSAT
HY-2B
Meteor-M3
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Atelier Moment Cinetique Paris 26 Novembre
2012
Les Vents de Surface Diffusiométriques
• Bentamy, A., D. Croize-Fillon, and C. Perigaud, 2008: Characterization of ASCAT measurements based on buoy and QuikSCAT wind vector observations, Ocean Sci., 4, 265–274.
• Bentamy, A.; D. Croize-Fillon, P. Queffeulou; C. Liu, H. Roquet, 2009: Evaluation of high-resolution surface wind products at global and regional scales. Journal of Operational Oceanography, vol. 2, 15-27(13).
• Bentamy, A., S. A. Grodsky, J. A. Carton, D. Croizé-Fillon, and B. Chapron, 2012: Matching ASCAT and QuikSCAT Winds, J. Geoph. Res., doi:10.1029/2011JC007479
• Grodsky S. A., V. N. Kudryavtsev, A. Bentamy, J. A. Carton, and B. Chapron, 2012: Does direct impact of SST on short wind waves matter for scatterometry?, Geophys. Res. Letters, doi:10.1029/2012GL052091
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Atelier Moment Cinetique Paris 26 Novembre
2012
The main scatterometer measurements are the backscatter coefficients calculated as a ratio between the emitted power Pe and the received one Pr :
: the wavelength, G the antenna gain, A the radar footprint, R the distance between the sensor and the reached target.
e
r
APGPR
22
430 )4(
Scatterometers are active microwave sensors: they send out a signal and measure how much of that signal returns after interacting with the target. Microwaves are Bragg scattered by short water waves; the fraction of energy returned to the satellite (backscatter) is a function of wind speed and wind direction.
Scatterometer measurement
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Scatterometer Calibration
Retrieving Surface Winds from Backscatter Coefficient Measurements is not Trivial
Atelier Moment Cinetique Paris 26 Novembre
2012
Calibration Procedure: Determination of Geophysical Model Function (GMF):
° = f(U,, , P,fc, ….)
),,,(;2coscos 2100 fcPUAAAAA JJ
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PORSEC 2012 Kochi Tutorial
),,,(;2coscos 2100 fcPUAAAAA JJ GMF :
Scatterometer Geophysical Relationships
Buoy Wind Speed Range 8m/s
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PORSEC 2012 Kochi Tutorial
),,,(;2coscos 2100 fcPUAAAAA JJ GMF :
Scatterometer Geophysical Relationships
Buoy Wind Speed Range 3m/s
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PORSEC 2012 Kochi Tutorial
),,,(;2coscos 2100 fcPUAAAAA JJ GMF :
Scatterometer Geophysical Relationships
Buoy Wind Speed Range 12m/s
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mer
Atelier Moment Cinetique Paris 26 Novembre 2012
ASCAT / QuikSCAT (Bentamy et al, 2011)
Study Period: April 2007 – November 2009
Focus : November 2008 – November 2009
ASCAT
•Data Source: OSI SAF / KNMI
•Products: L1b & L2b 25 & L2b 12.5
•GMF : CMOD5 and CMOD5n
•Wind retrieval: Selected solution
•Data selection:
All WVC
Wind Speed : 0 – 50m/s
Wind direction : 0° – 360°
Quality flags
QuikSCAT / QuikSCAT V3
•Data Source: PODAAC / JPL
•Products: L1b & L2b 25 / L2b 12.5
•GMF : QSCAT-1/F13 / QuikSCAT (Ku2011)
•Wind retrieval: Selected solution
•Data selection:
All WVC
Wind Speed : 0 – 50m/s
Wind direction : 0° – 360°
Quality flags / New Rain flags
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Atelier Moment Cinetique Paris 26 Novembre 2012
Local Assessment for ASCAT/QSCAT Collocated Data
Comparisons with NDBC buoy hourly measurements Comparisons with NDBC buoy hourly measurements
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Atelier Moment Cinetique Paris 26 Novembre 2012
Global ComparisonsBias (top), STD (middle), and Correlation (bottom) of collocated
QuikScat and ASCAT winds.
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Analysis of ASCAT and QSCAT Differences
Atelier Moment Cinetique Paris 26 Novembre
2012
Wind speed difference. QuikSCAT rain flag and MRP<0.05 are applied
Spatial distribution of the time mean
Wind speed difference after applying the correction function
Histogram of wind speed difference before (gray bar) and after (empty bar) applying of dW
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lfre
merMean Difference of Wind Speeds:
QSCAT / ASCAT / ECMWF / ERA Interim
Atelier Moment Cinetique Paris 26 Novembre
2012
QSCAT
ASCAT
ECMWF ERAI
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Mean Difference of Wind Components : QSCAT / ASCAT / ECMWF
Atelier Moment Cinetique Paris 26 Novembre
2012
| QSCAT | - | ASCAT |
| QSCAT | - | ECMWF |
| ASCAT | - | ECMWF |
Zonal Meridional
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Mean Difference of Wind Components: QSCAT / ASCAT / ERA Interim
Atelier Moment Cinetique Paris 26 Novembre
2012
|QSCAT| - | ASCAT |
| QSCAT | - | ERAI |
| ASCAT | - | ERAI |
Zonal Meridional
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Zonal Means of Wind Components Within 3 degree of 140°W
Atelier Moment Cinetique Paris 26 Novembre
2012
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16
High Wind Field Spatial and Temporal Resolution
QuikSCAT
SSMI
SSMI
SSMIAMSR-E
TMI
Jason
METOP
Objectives
Estimation of high spatial and temporal resolution of surface wind fields (wind vector and wind stress) using ECMWF Numerical Weather analysis outputs with high remotely sensed surface parameters.
Set-up and carry-out a demonstration experiment, to produce in near real-time merged wind fields : 6-hourly, 0.25° x 0.25°6-hourly, 0.25° x 0.25°
Assess the quality of derived blended wind fields at near shore and offshore areas.
E.U. MyOcean-1/2 ProjectsE.U. MyOcean-1/2 Projects
Operational ECMWF Analysis
Atelier Moment Cinetique Paris 26 Novembre
2012
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17
Objective Method
Objective Method : External Drift
Wind Observations (U) are from NRT Scatterometer and SSM/I
External Data (S) are from ECMWF analysis.
Assumption : E(U(X,t)) = a + b*S(X,t)
n
i
n
i
j
n
i
i
SiiS
i
jSjji
1
1
1
21
)0()(
1
02)()0,(),(
))exp(1(),(b
tchath p
The space and time correlation is
parameterized by
Atelier Moment Cinetique Paris 26 Novembre
2012
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AMS Conference 20 - 24 August 2007 Portland 18
Blended Surface Wind Fields
Method : Objective OI (Bentamy et al, 2007; 2009)
Results :
6-hourly global
wind vector
0.25°×0.25°
May 4th 2008. 00h:00
May 4th 2008. 06h:00
Atelier Moment Cinetique Paris 26 Novembre
2012
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Atelier Moment Cinetique Paris 26 Novembre
2012
Evaluation Versus QuikSCAT (off-line) Wind ObservationsJanuary 2005 (Bentamy et al, 2009)
QuikSCAT – Blended
Bias Rms
QuikSCAT – ECMWF
Bias RmsW
U
V