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TU4.L10 - A REVISED GEOPHYSICAL MODEL FUNCTION FOR THE ADVANCED SCATTEROMETER (ASCAT) AT NOAA/NESDIS
 

TU4.L10 - A REVISED GEOPHYSICAL MODEL FUNCTION FOR THE ADVANCED SCATTEROMETER (ASCAT) AT NOAA/NESDIS

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  • match iwrap gmf trend and adjust for b0 bias relative ti quikscat/ascat mu
  • 3.79 5.06
  • Loss of QS Significant reduction in detection capability of HF conditions Will lose 85% of current capability Lose ability to consistently verify HF warnings 3.61 4.51 5.25 0.25

TU4.L10 - A REVISED GEOPHYSICAL MODEL FUNCTION FOR THE ADVANCED SCATTEROMETER (ASCAT) AT NOAA/NESDIS TU4.L10 - A REVISED GEOPHYSICAL MODEL FUNCTION FOR THE ADVANCED SCATTEROMETER (ASCAT) AT NOAA/NESDIS Presentation Transcript

  • A Revised Geophysical Model Function for the Advanced Scatterometer (ASCAT) at NOAA/NESDIS Seubson Soisuvarn, Zorana Jelenak, Paul S. Chang, and Qi Zhu NOAA/NESDIS/STAR-UCAR IGARSS 2010, July 25-30, Honolulu, Hawaii, USA
  • Introduction
    • ASCAT measures radar backscatter (sigma0) using C-band vertically polarized fan-beam antennas - multiple incidence angles (~25°-65°)
    • Operational ASCAT winds retrievals is based on CMOD5.n model function and it shows clearly underestimates high wind speeds
      • Hurricane force wind detection from ASCAT is very rare
    Can ASCAT high wind speed retrievals be improved?
  • What do we know
    • Scatterometer wind retrievals are dependent on Geophysical Model Function (GMF) that relates backscatter (Sigma0) to ocean surface wind fields
    • Satellite C-band V-Pol Sigma0 collocation data at high winds are not currently sufficient to build empirical geophysical model function
      • Winds are not quite uniformly distributed in all directions
    • C-band V-Pol Sigma0 measurements for high winds are available from Airborne scatterometer (IWRAP) but at limited incidence angles and much higher resolution than satellite measurements
  • Study Approach
    • The ASCAT operational GMF (CMOD5.n) is written in harmonic terms:
    • ASCAT/QuikSCAT collocations show B 0 is biased high at high wind speeds.
    • Replace B 0 term with a new B 0 and assuming B 1 and B 2 are modeled correctly
      • Not a new idea (Jones et. al – TRMM PR GMF, IGARSS’03, ’04)
      • New B 0 is determined based on a linear characteristic of an airborne scatterometer GMF (IWRAP)
        • Replace B 0 only at higher winds
    Hersbach, et al., J. Geophys. Res. (2007)
  • Measured and Model Sigma0 dependence on wind vector at 30 deg incidence Relative wind direction (Degree) Sigma0 ASCAT/QuikSCAT matchu-ups @ 30 ° incidence 5m/s 9m/s 12m/s 15m/s 17m/s 20m/s CMOD5n B 0 “ True” B 0
  • C-Band V-pol Saturation wind speeds
    • IWRAP GMF is valid at 29 ° , 34 ° , 40 ° and 50 ° incidence and 25-65 m/s
    • The B 0 is written in the form:
    • U 10Nsat is defined as the wind speed where B 0 reaches its maximum value:
    Fernandez, et al., J. Geophys. Res. (2006) Fernandez, et al., J. Geophys. Res. (2006) cmod5n is not saturate beyond 40 ° incidence IWRAP saturation wind speed New Saturation Wind speed
  • High wind speed B 0 ; Incidence: 50 deg B 0 vs wind speed IWRAP New B 0 U 10Nsat =61.5 m/s vs wind speed U 10Nsat =61.5 m/s New B 0 IWRAP
  • CMOD5n vs New B 0 CMOD5n B 0 New B 0 Wind Speed (m/s) B 0 25° 30° 40° 50° 60° 65°
  • Sigma0 Model vs. Measurements Measured Sigma0 (dB) Calculated Sigma0 (dB) CMOD5.n New GMF Fore-beam Mid-beam Aft-beam Fore-beam Mid-beam Aft-beam
  • ASCAT vs QuikSCAT speed (before) QuikSCAT Wind Speeds ASCAT Wind Speeds Cumulative distribution curve
  • ASCAT vs QuikSCAT speed (after) QuikSCAT Wind Speeds ASCAT Wind Speeds Cumulative distribution curve
  • ASCAT vs QuikSCAT direction (before) QuikSCAT Wind Directions ASCAT Wind Directions
  • ASCAT vs QuikSCAT direction (after) QuikSCAT Wind Directions ASCAT Wind Directions
  • Across Swath Speed Biases (before) 2 m/s reference line
  • Across Swath Speed Biases (after) 2 m/s reference line
  • Across Swath Speed RMS errors (before) 2 m/s reference line
  • Across Swath Speed RMS errors (after) 2 m/s reference line
  • Operational ASCAT QuikSCAT Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific
  • Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific New ASCAT QuikSCAT
  • 1000km 2000km 3000km Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific QuikSCAT New ASCAT
  • Gale Force Wind Frequency Storm Force Wind Frequency QuikSCAT Gale Force Wind Frequency Storm Force Wind Frequency Operational ASCAT Hurricane Force Wind Frequency Hurricane Force Wind Frequency
  • Gale Force Wind Frequency Storm Force Wind Frequency New ASCAT Hurricane Force Wind Frequency Gale Force Wind Frequency Storm Force Wind Frequency Hurricane Force Wind Frequency Operational ASCAT
  • Operational ASCAT Sonde Wind Speed 28.8m/s SFMR 28 m/s Operational ASCAT 22 m/s
  • New ASCAT Sonde Wind Speed 28.8m/s SFMR 28 m/s New ASCAT 25 m/s
  • Conclusions
    • New High wind ASCAT GMF was developed
      • B 0 was modified in CMOD5.n
        • Matching IWRAP GMF high wind trend and correcting for observed B 0 biases
    • New ASCAT high wind speed retrievals are improved
      • Bias and RMS wind speed errors are compared better to QuikSCAT and SFMR
      • New ASCAT wind speed retrievals are still biased low but resultant biases are smaller
      • Improve storm and hurricane force wind detection
    • Next Step:
    • Transition new ASCAT winds product into operations (Soon)
  • BACK UP
  • Operational wind speed histogram
  • New wind speed histogram
  • Operational ASCAT KNMI KNMI Mean bias = -3.77 m/s Mean STD = 1.01 m/s
  • New ASCAT KNMI KNMI Mean bias = -2.38 m/s Mean STD = 0.98 m/s
  • Model vs. Measurement @ 30° incidence CMOD5.n New
  • Measured vs CMOD5.n 30 deg
  • Measured vs CMOD5.n 40 deg
  • Measured vs CMOD5.n 50 deg
  • Measured vs CMOD5.n 60 deg
  • Can ASCAT high wind speed retrievals be improved? Hurricane Force Observations Oct’07 ~ May’08
    • ASCAT underestimate high wind speeds in comparison to QuikSCAT
      • Hurricane force wind detection from ASCAT is very rare
    195 168 2 38 4 15
    • Loss of QuikSCAT data could possibly result in 80-90% reduction in detection of hurricane force winds
    • Necessary to investigate improvement in ASCAT wind retrievals are in order to support wind warning and forecast products for extreme winter ocean storms
  • Hurricane Force Observations ( Oct’07 ~ May’08 ) 212 188 2 39 38 19
  • Operational ASCAT wind product detects STORM force wind. One wind warning category lower than the actual winds. North Atlantic Extratropical Storm Example QuikSCAT & New ASCAT wind products detects HF wind. New ASCAT Operational ASCAT QuikSCAT
  •  
  • Resolution effect Ernesto Rodriguez OVWST meeting 2009
  • Smoothing
  • B0 vs wind speed