EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS
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EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS

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EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS EVALUATIONS OF WIND VECTORS OBSERVED BY ASCAT USING STATISTICAL DISTRIBUTIONS Presentation Transcript

  • Evaluation of Wind Vectors observed by ASCAT using Statistical Distributions
    • Naoto EBUCHI
    • Institute of Low Temperature Science, Hokkaido University
    • [email_address]
    MetOp-A
  • Outline
    • 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
  • Monthly Report on Buoy Comparison by KNMI
  • Buoy 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
    NDBC NDBC TAO PIRATA KEO RAMA WHOI
  • Comparison of ASCAT Winds with Buoy Data
    • # Bias RMS Correlation
    • Wind Speed (m/s) 27,247 -0.15 1.42 0.885
    • Wind 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
  • Calculation of Global Statistics of ASCAT Wind Speeds and Directions
    • ASCAT 25 km Swath Products (L2)
    • 1 Jan. 2010 – 31 Dec. 2010 (1 year)
    • Global ocean, 60 o S – 60 o N
    • Collocated ECMWF winds (Non-EN wind)
    • 156 million data points
  • ASCAT Global Wind Speed Histograms
    • Period: 1 Jan. 2010 – 31 Dec. 2010 (1 year)
    • Area: global ocean, 60 o S – 60 o N
    • Bin size: 1 m/s
  • ECMWF Wind Speed Histograms
    • Collocated with ASCAT observations
  • Statistics of ASCAT Wind Speed Distribution ASCAT NWP
  • Statistics of ASCAT Wind Speed Distribution ASCAT NWP 12.5 km Product
  • ASCAT 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 ECMWF ASCAT
  • Normalized ASCAT Wind Direction Histograms WVC# 1-3 WVC# 4-6 WVC# 7-9 WVC# 10-12 WVC# 13-15 WVC# 16-18 WVC# 19-21 Descending Ascending Normalized (ASCAT/NWP), Left Swath, Wind Speed Range: 7-9 m/s
  • Wind Speed Dependence of Normalized Wind Direction Histograms (Outer Cells) Normalized (ASCAT/NWP), WVC#: 1-3 (Left Outer Swath) Descending Ascending 3-5 m/s 5-7 m/s 7-9 m/s 9-11 m/s 11-13 m/s 13-15 m/s
  • Wind Speed Dependence of Normalized Wind Direction Histograms (Mid Cells) Normalized (ASCAT/NWP), WVC#: 10-12 (Left Mid Swath) Descending Ascending 3-5 m/s 5-7 m/s 7-9 m/s 9-11 m/s 11-13 m/s 13-15 m/s
  • Wind Speed Dependence of Normalized Wind Direction Histograms (Inner Cells) Normalized (ASCAT/NWP), WVC#: 19-21 (Left Inner Swath) Descending Ascending 3-5 m/s 5-7 m/s 7-9 m/s 9-11 m/s 11-13 m/s 13-15 m/s
  • Applications to data from Oceansat-II scatterometer Oceansat-II Scatteromter (OSCAT) Ku-band (13.51 GHz) Scanning dual pencil beam VV and HH pol 50 km resolution 1800 km swath
  • Comparison of OSCAT Winds with Buoy Data
    • # Bias RMS Correlation
    • Wind Speed (m/s) 8,938 0.56 1.65 0.893
    • Wind 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
  • OSCAT Global Wind Speed Histograms
    • Period: 1 Jan. 2010 – 31 Dec. 2010 (1 year)
    • Area: global ocean, 60 o S – 60 o N
    • Bin size: 1 m/s
  • ECMWF Wind Speed Histograms
    • Collocated with OSCAT observations
  • Statistics of OSCAT Wind Speed Distribution OSCAT Asc NWP OSCAT Dec ECMWF Asc ECMWF Dec
  • OSCAT 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# 16-18 WVC# 10-12 ECMWF OSCAT
  • Summary
    • 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.
  •  
  • Comparison of wind speed
  • Residuals of Wind Speed and Direction
  • Residuals of Wind Speed and Direction Binning wind speed = (U buoy + U scat )/2
  • Dependence of Wind Speed Residual on Wave Parameter Significant Wave Height Inverse Wave Age Correlation Coefficient = 0.300 Correlation Coefficient = -0.311
  • Comparison of wind speed OSCAT
  • Residuals of Wind Speed and Direction Binning wind speed = (U buoy + U scat )/2 OSCAT
  • Statistics of NSCAT Wind Speed Distribution ASCAT ASCAT ASCAT ASCAT (Ebuchi, J. Oceanogr ., 2000)
  • Statistics of QSCAT Wind Speed Distribution ASCAT ASCAT ASCAT ASCAT Ascending Descending
  • Histograms of ERS-1 Wind Directions CMOD-4 CMOD-IFR2 (Ebuchi & Graber, JGR , 1998)
  • Histograms of NSCAT Wind Directions (Ebuchi, JGR , 1999)
  • Histograms of QSCAT Wind Directions (Ebuchi, Proc. IGARSS 2000 , 2000)
  • Rough estimation of incidence angle error
    • Based on the SASS-2 GMF (Wentz et al., 1984)
    • At an incidence angle of  = 57 o , VV-pol., and wind speed of U 10 = 10 m/s,
    • d  0 / d  = – 0.3 dB
    • d  0 / d U 10  = 0.7 dB
    • An error of 1 o in incidence angle may cause an error of 0.4 m/s in wind speed.