A Revised Geophysical Model Function for the Advanced Scatterometer (ASCAT) at NOAA/NESDIS Seubson Soisuvarn, Zorana Jelen...
Introduction <ul><li>ASCAT measures radar backscatter (sigma0) using C-band vertically polarized fan-beam antennas - multi...
What do we know <ul><li>Scatterometer wind retrievals are dependent on Geophysical Model Function (GMF) that relates backs...
Study Approach <ul><li>The ASCAT operational GMF (CMOD5.n) is written in harmonic terms: </li></ul><ul><li>ASCAT/QuikSCAT ...
Measured and Model Sigma0 dependence on wind vector at 30 deg incidence Relative wind direction (Degree) Sigma0 ASCAT/Quik...
C-Band V-pol Saturation wind speeds <ul><li>IWRAP GMF is valid at 29 ° , 34 ° , 40 °  and 50 °  incidence and 25-65 m/s </...
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....
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...
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 Operati...
Gale Force Wind Frequency Storm Force Wind Frequency New ASCAT Hurricane Force Wind Frequency Gale Force Wind Frequency St...
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   <ul><li>New High wind ASCAT GMF was developed </li></ul><ul><ul><li>B 0  was modified in CMOD5.n </li></ul><...
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 <ul><li>ASCAT underestimate...
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 Atla...
 
Resolution effect Ernesto Rodriguez OVWST meeting 2009
Smoothing
B0 vs wind speed
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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

    1. 1. 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
    2. 2. Introduction <ul><li>ASCAT measures radar backscatter (sigma0) using C-band vertically polarized fan-beam antennas - multiple incidence angles (~25°-65°) </li></ul><ul><li>Operational ASCAT winds retrievals is based on CMOD5.n model function and it shows clearly underestimates high wind speeds </li></ul><ul><ul><li>Hurricane force wind detection from ASCAT is very rare </li></ul></ul>Can ASCAT high wind speed retrievals be improved?
    3. 3. What do we know <ul><li>Scatterometer wind retrievals are dependent on Geophysical Model Function (GMF) that relates backscatter (Sigma0) to ocean surface wind fields </li></ul><ul><li>Satellite C-band V-Pol Sigma0 collocation data at high winds are not currently sufficient to build empirical geophysical model function </li></ul><ul><ul><li>Winds are not quite uniformly distributed in all directions </li></ul></ul><ul><li>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 </li></ul>
    4. 4. Study Approach <ul><li>The ASCAT operational GMF (CMOD5.n) is written in harmonic terms: </li></ul><ul><li>ASCAT/QuikSCAT collocations show B 0 is biased high at high wind speeds. </li></ul><ul><li>Replace B 0 term with a new B 0 and assuming B 1 and B 2 are modeled correctly </li></ul><ul><ul><li>Not a new idea (Jones et. al – TRMM PR GMF, IGARSS’03, ’04) </li></ul></ul><ul><ul><li>New B 0 is determined based on a linear characteristic of an airborne scatterometer GMF (IWRAP) </li></ul></ul><ul><ul><ul><li>Replace B 0 only at higher winds </li></ul></ul></ul>Hersbach, et al., J. Geophys. Res. (2007)
    5. 5. 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
    6. 6. C-Band V-pol Saturation wind speeds <ul><li>IWRAP GMF is valid at 29 ° , 34 ° , 40 ° and 50 ° incidence and 25-65 m/s </li></ul><ul><li>The B 0 is written in the form: </li></ul><ul><li>U 10Nsat is defined as the wind speed where B 0 reaches its maximum value: </li></ul>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
    7. 7. 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
    8. 8. CMOD5n vs New B 0 CMOD5n B 0 New B 0 Wind Speed (m/s) B 0 25° 30° 40° 50° 60° 65°
    9. 9. 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
    10. 10. ASCAT vs QuikSCAT speed (before) QuikSCAT Wind Speeds ASCAT Wind Speeds Cumulative distribution curve
    11. 11. ASCAT vs QuikSCAT speed (after) QuikSCAT Wind Speeds ASCAT Wind Speeds Cumulative distribution curve
    12. 12. ASCAT vs QuikSCAT direction (before) QuikSCAT Wind Directions ASCAT Wind Directions
    13. 13. ASCAT vs QuikSCAT direction (after) QuikSCAT Wind Directions ASCAT Wind Directions
    14. 14. Across Swath Speed Biases (before) 2 m/s reference line
    15. 15. Across Swath Speed Biases (after) 2 m/s reference line
    16. 16. Across Swath Speed RMS errors (before) 2 m/s reference line
    17. 17. Across Swath Speed RMS errors (after) 2 m/s reference line
    18. 18. Operational ASCAT QuikSCAT Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific
    19. 19. Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific New ASCAT QuikSCAT
    20. 20. 1000km 2000km 3000km Mean Wind Speed Field 2007-2009 Winter Seasons - North Pacific QuikSCAT New ASCAT
    21. 21. 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
    22. 22. 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
    23. 23. Operational ASCAT Sonde Wind Speed 28.8m/s SFMR 28 m/s Operational ASCAT 22 m/s
    24. 24. New ASCAT Sonde Wind Speed 28.8m/s SFMR 28 m/s New ASCAT 25 m/s
    25. 25. Conclusions <ul><li>New High wind ASCAT GMF was developed </li></ul><ul><ul><li>B 0 was modified in CMOD5.n </li></ul></ul><ul><ul><ul><li>Matching IWRAP GMF high wind trend and correcting for observed B 0 biases </li></ul></ul></ul><ul><li>New ASCAT high wind speed retrievals are improved </li></ul><ul><ul><li>Bias and RMS wind speed errors are compared better to QuikSCAT and SFMR </li></ul></ul><ul><ul><li>New ASCAT wind speed retrievals are still biased low but resultant biases are smaller </li></ul></ul><ul><ul><li>Improve storm and hurricane force wind detection </li></ul></ul><ul><li>Next Step: </li></ul><ul><li>Transition new ASCAT winds product into operations (Soon) </li></ul>
    26. 26. BACK UP
    27. 27. Operational wind speed histogram
    28. 28. New wind speed histogram
    29. 29. Operational ASCAT KNMI KNMI Mean bias = -3.77 m/s Mean STD = 1.01 m/s
    30. 30. New ASCAT KNMI KNMI Mean bias = -2.38 m/s Mean STD = 0.98 m/s
    31. 31. Model vs. Measurement @ 30° incidence CMOD5.n New
    32. 32. Measured vs CMOD5.n 30 deg
    33. 33. Measured vs CMOD5.n 40 deg
    34. 34. Measured vs CMOD5.n 50 deg
    35. 35. Measured vs CMOD5.n 60 deg
    36. 36. Can ASCAT high wind speed retrievals be improved? Hurricane Force Observations Oct’07 ~ May’08 <ul><li>ASCAT underestimate high wind speeds in comparison to QuikSCAT </li></ul><ul><ul><li>Hurricane force wind detection from ASCAT is very rare </li></ul></ul>195 168 2 38 4 15 <ul><li>Loss of QuikSCAT data could possibly result in 80-90% reduction in detection of hurricane force winds </li></ul><ul><li>Necessary to investigate improvement in ASCAT wind retrievals are in order to support wind warning and forecast products for extreme winter ocean storms </li></ul>
    37. 37. Hurricane Force Observations ( Oct’07 ~ May’08 ) 212 188 2 39 38 19
    38. 38. 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
    39. 40. Resolution effect Ernesto Rodriguez OVWST meeting 2009
    40. 41. Smoothing
    41. 42. B0 vs wind speed

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