EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS
Transcript of EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS
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Evaluation of Wind Vectors observed by Evaluation of Wind Vectors observed by ASCAT using Statistical DistributionsASCAT using Statistical Distributions
Naoto EBUCHIInstitute of Low Temperature Science, Hokkaido University
MetOp-A
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OutlineOutline
• Comparison of ASCAT wind vectors with data from ocean buoys
• Assessment of statistical distributions of ASCAT wind speeds and directions – Global wind speed histograms– Directional distributions relative to antenna beams
• Applications to Oceansat-II scatterometer
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Monthly Report on Buoy Comparison Monthly Report on Buoy Comparison by KNMIby KNMI
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Buoy Data for Comparison with ASCATBuoy Data for Comparison with ASCAT
• Data Period- From 20 Nov. 2008 to 31 Dec. 2010
• Collocation- ∆r < 12.5 km, ∆t<10 min.
• Height and Stability Collections- Liu and Tang (1996) Code- 10-m height Neutral Equivalent Wind
NDBCNDBC
TAO
PIRATA
KEO
RAMA WHOI
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Comparison of ASCAT Winds with Buoy DataComparison of ASCAT Winds with Buoy Data
# Bias RMS CorrelationWind Speed (m/s) 27,247 -0.15 1.42 0.885Wind Direction (deg.)
U > 0 m/s 26,976 3.0 26.2 0.957 U > 3 m/s 23,750 2.7 17.4 0.979 U > 5 m/s 18,672 2.7 14.1 0.985
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Calculation of Global Statistics of Calculation of Global Statistics of ASCAT Wind Speeds and DirectionsASCAT Wind Speeds and Directions
• ASCAT 25 km Swath Products (L2)• 1 Jan. 2010 – 31 Dec. 2010 (1 year)• Global ocean, 60oS – 60oN• Collocated ECMWF winds (Non-EN wind)• 156 million data points
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ASCAT Global Wind Speed HistogramsASCAT Global Wind Speed Histograms
Period: 1 Jan. 2010 – 31 Dec. 2010 (1 year)Area: global ocean, 60oS – 60oNBin size: 1 m/s
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ECMWF Wind Speed HistogramsECMWF Wind Speed Histograms
Collocated with ASCAT observations
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Statistics of ASCAT Wind Speed DistributionStatistics of ASCAT Wind Speed Distribution
ASCAT
NWP
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Statistics of ASCAT Wind Speed DistributionStatistics of ASCAT Wind Speed Distribution
ASCAT
NWP
12.5 kmProduct
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ASCAT Wind Direction HistogramsASCAT Wind Direction Histograms
Left Swath, Wind Speed Range: 7-9 m/s, Descending Paths
WVC# 1-3 WVC# 4-6 WVC# 7-9 WVC# 10-12
WVC# 13-15 WVC# 16-18 WVC# 19-21
ECMWFASCAT
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Normalized ASCAT Wind Direction HistogramsNormalized ASCAT Wind Direction HistogramsWVC# 1-3 WVC# 4-6 WVC# 7-9 WVC# 10-12
WVC# 13-15 WVC# 16-18 WVC# 19-21
DescendingAscending
Normalized (ASCAT/NWP), Left Swath, Wind Speed Range: 7-9 m/s
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Wind Speed Dependence of Normalized Wind Direction Wind Speed Dependence of Normalized Wind Direction Histograms (Outer Cells)Histograms (Outer Cells)
Normalized (ASCAT/NWP), WVC#: 1-3 (Left Outer Swath)
DescendingAscending
3-5 m/s 5-7 m/s 7-9 m/s
9-11 m/s 11-13 m/s 13-15 m/s
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Wind Speed Dependence of Normalized Wind Direction Wind Speed Dependence of Normalized Wind Direction Histograms (Mid Cells)Histograms (Mid Cells)
Normalized (ASCAT/NWP), WVC#: 10-12 (Left Mid Swath)
DescendingAscending
3-5 m/s 5-7 m/s 7-9 m/s
9-11 m/s 11-13 m/s 13-15 m/s
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Wind Speed Dependence of Normalized Wind Direction Wind Speed Dependence of Normalized Wind Direction Histograms (Inner Cells)Histograms (Inner Cells)
Normalized (ASCAT/NWP), WVC#: 19-21 (Left Inner Swath)
DescendingAscending
3-5 m/s 5-7 m/s 7-9 m/s
9-11 m/s 11-13 m/s 13-15 m/s
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Applications to data Applications to data from Oceansat-II scatterometerfrom Oceansat-II scatterometer
Oceansat-II Scatteromter(OSCAT)Ku-band (13.51 GHz)Scanning dual pencil beamVV and HH pol50 km resolution1800 km swath
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Comparison of Comparison of OSCATOSCAT Winds with Buoy Data Winds with Buoy Data
# Bias RMS CorrelationWind Speed (m/s) 8,938 0.56 1.65 0.893Wind Direction (deg.)
U > 0 m/s 8,835 -0.2 32.4 0.938 U > 3 m/s 7,550 -0.3 22.3 0.968 U > 5 m/s 6,130 -0.4 14.1 0.977
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OSCATOSCAT Global Wind Speed Histograms Global Wind Speed Histograms
Period: 1 Jan. 2010 – 31 Dec. 2010 (1 year)Area: global ocean, 60oS – 60oNBin size: 1 m/s
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ECMWF Wind Speed HistogramsECMWF Wind Speed Histograms
Collocated with OSCAT observations
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Statistics of Statistics of OSCATOSCAT Wind Speed Distribution Wind Speed Distribution
OSCATAsc
NWPOSCATDec
ECMWFAscECMWFDec
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OSCATOSCAT Wind Direction Histograms Wind Direction Histograms
Left Swath, Wind Speed Range: 7-9 m/s, Ascending Paths
WVC# 1-3 WVC# 4-6 WVC# 7-9
WVC# 13-15 WVC# 16-18WVC# 10-12
ECMWFOSCAT
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SummarySummary
• ASCAT wind speeds and directions agrees well with buoy observations in general.
• ASCAT global wind speed histogram varies with cross-track cell location. This trend is clearly represented by statistical parameters, such as standard deviation, skewness and kurtosis.
• Directivity relative to the antenna beams is discernible for ASCAT wind directions.
• At low wind speeds and the outer cells (high incidence), most of wind vectors aligned to the flight direction or mid-beam direction.
• These results suggest the needs for further refinements of the wind retrieval algorithms and the C-band GMF.
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Comparison of wind speedComparison of wind speed
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Residuals of Wind Speed and DirectionResiduals of Wind Speed and Direction
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Residuals of Wind Speed and DirectionResiduals of Wind Speed and Direction
Binning wind speed = (Ubuoy + Uscat)/2
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Dependence of Wind Speed Residual Dependence of Wind Speed Residual on Wave Parameteron Wave Parameter
Significant Wave Height Inverse Wave Age
Correlation Coefficient = 0.300 Correlation Coefficient = -0.311
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Comparison of wind speedComparison of wind speedOSCAT
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Residuals of Wind Speed and DirectionResiduals of Wind Speed and Direction
Binning wind speed = (Ubuoy + Uscat)/2
OSCAT
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Statistics of Statistics of NSCATNSCAT Wind Speed Wind Speed DistributionDistribution
ASCAT
ASCAT
ASCAT
ASCAT
(Ebuchi, J. Oceanogr., 2000)
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Statistics of Statistics of QSCATQSCAT Wind Speed Distribution Wind Speed Distribution
ASCAT
ASCAT
ASCAT
ASCAT
Ascending
Descending
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Histograms of Histograms of ERS-1ERS-1 Wind Directions Wind DirectionsCMOD-4 CMOD-IFR2
(Ebuchi & Graber, JGR, 1998)
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Histograms of Histograms of NSCATNSCAT Wind Directions Wind Directions
(Ebuchi, JGR, 1999)
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Histograms of Histograms of QSCATQSCAT Wind Directions Wind Directions
(Ebuchi, Proc. IGARSS 2000, 2000)
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Rough estimation of incidence angle errorRough estimation of incidence angle error
• Based on the SASS-2 GMF (Wentz et al., 1984)
• At an incidence angle of θ = 57o, VV-pol., and wind speed of U10 = 10 m/s,
d σ 0 / d θ = – 0.3 dB
d σ 0 / d U10 = 0.7 dB
• An error of 1o in incidence angle may cause an error of 0.4 m/s in wind speed.