Atelier Moment Cinetique Paris 26 Novembre 2012 Les Vents de Surface Diffusiométriques 1992 2020...

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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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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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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


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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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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Local Assessment for ASCAT/QSCAT Collocated Data

Comparisons with NDBC buoy hourly measurements Comparisons with NDBC buoy hourly measurements

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Global ComparisonsBias (top), STD (middle), and Correlation (bottom) of collocated

QuikScat and ASCAT winds.

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Analysis of ASCAT and QSCAT Differences


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


2012

QSCAT

ASCAT

ECMWF ERAI

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Zonal Means of Wind Components Within 3 degree of 140°W


2012

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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


2012

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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


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


2012

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2012

Evaluation Versus QuikSCAT (off-line) Wind ObservationsJanuary 2005 (Bentamy et al, 2009)

QuikSCAT – Blended

Bias Rms

QuikSCAT – ECMWF

Bias RmsW

U

V

Atelier Moment Cinetique Paris 26 Novembre 2012 Les Vents de Surface Diffusiométriques 1992 2020...

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