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Les Vents de Surface Diffusiométriques

Les Vents de Surface Diffusiométriques. 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.

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Les Vents de Surface Diffusiométriques

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  1. Atelier Moment Cinetique Paris 26 Novembre 2012 Les Vents de Surface Diffusiométriques

  2. 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

  3. Atelier Moment Cinetique Paris 26 Novembre 2012 Scatterometer measurement • 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. • 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.

  4. Atelier Moment Cinetique Paris 26 Novembre 2012 Scatterometer Calibration • Retrieving Surface Winds from Backscatter Coefficient Measurements is not Trivial • Calibration Procedure: Determination of Geophysical Model Function (GMF): • ° = f(U,, , P,fc, ….)

  5. PORSEC 2012 Kochi Tutorial Scatterometer Geophysical Relationships GMF : Buoy Wind Speed Range 8m/s

  6. PORSEC 2012 Kochi Tutorial Scatterometer Geophysical Relationships GMF : Buoy Wind Speed Range 3m/s

  7. PORSEC 2012 Kochi Tutorial Scatterometer Geophysical Relationships GMF : Buoy Wind Speed Range 12m/s

  8. 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

  9. Atelier Moment Cinetique Paris 26 Novembre 2012 Local Assessment for ASCAT/QSCAT Collocated Data • Comparisonswith NDBC buoyhourlymeasurements • Comparisons with NDBC buoy hourly measurements

  10. Atelier Moment Cinetique Paris 26 Novembre 2012 Global Comparisons • Bias (top), STD (middle), and Correlation (bottom) of collocated QuikScat and ASCAT winds.

  11. Atelier Moment Cinetique Paris 26 Novembre 2012 Analysis of ASCAT and QSCAT Differences • Wind speed difference. QuikSCAT rain flag and MRP<0.05 are applied • Wind speed difference after applying the correction function • Spatial distribution of the time mean • Histogram of wind speed difference before (gray bar) and after (empty bar) applying of dW

  12. Atelier Moment Cinetique Paris 26 Novembre 2012 Mean Difference of Wind Speeds: QSCAT / ASCAT / ECMWF / ERA Interim ECMWF ERAI QSCAT ASCAT

  13. Atelier Moment Cinetique Paris 26 Novembre 2012 Mean Difference of Wind Components : QSCAT / ASCAT / ECMWF Zonal Meridional | QSCAT | - | ASCAT | | QSCAT | - | ECMWF | | ASCAT | - | ECMWF |

  14. Atelier Moment Cinetique Paris 26 Novembre 2012 Mean Difference of Wind Components: QSCAT / ASCAT / ERA Interim Zonal Meridional |QSCAT| - | ASCAT | | QSCAT | - | ERAI | | ASCAT | - | ERAI |

  15. Atelier Moment Cinetique Paris 26 Novembre 2012 Zonal Means of Wind Components Within 3 degree of 140°W

  16. High Wind Field Spatial and Temporal Resolution Atelier Moment Cinetique Paris 26 Novembre 2012 QuikSCAT E.U. MyOcean-1/2 Projects METOP SSMI 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-timemerged wind fields : 6-hourly, 0.25° x 0.25° • Assess the quality of derived blended wind fields at near shore and offshore areas. SSMI TMI SSMI Jason AMSR-E Operational ECMWF Analysis 16

  17. Objective Method Atelier Moment Cinetique Paris 26 Novembre 2012 • 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) • The space and time correlation is parameterized by 17

  18. Blended Surface Wind Fields Atelier Moment Cinetique Paris 26 Novembre 2012 • Method : Objective OI (Bentamy et al, 2007; 2009) May 4th 2008. 00h:00 Results : 6-hourly global wind vector 0.25°×0.25° May 4th 2008. 06h:00 AMS Conference 20 - 24 August 2007 Portland 18

  19. 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 Rms W U V

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