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Airborne Measurements of Ocean Backscatter

Daniel Esteban Fernandez. Airborne Measurements of Ocean Backscatter. Acknowledgements: NOAA NESDIS Office Research & Applications NOAA Aircraft Operations Center University of Massachusetts. Outline. IWRAP Description and measurement technique

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Airborne Measurements of Ocean Backscatter

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  1. Daniel Esteban Fernandez Airborne Measurements of Ocean Backscatter Acknowledgements: NOAA NESDIS Office Research & Applications NOAA Aircraft Operations Center University of Massachusetts

  2. Outline • IWRAP • Description and measurement technique • Scatterometry Geophysical Model Functions (GMFs) • Methodology • Dual-band (C and Ku), dual-polarized (H and V) GMFs from IWRAP measurements

  3. IWRAP Measurement Technique • Reflectivity and Doppler profiles – four beams, two frequencies (C and Ku), two polarizations (H and V) –simultaneously. • High-resolution surface and volume backscatter

  4. IWRAP Designed to Investigate… Hurricane Katrina, August 28 th, 2005

  5. Summary of datasets • Flown during 2002, 2003, 2004 and 2005 Hurricane seasons, and the 2003 and 2005 Winter Storm experiments: 70 missions, including flights through hurricanes Gustav, Isidore, and Lili (2002), Fabian and Isabel (2003), Frances and Ivan (2004), Ophelia and Rita (2005), as well as several TDs, TSs and extra-tropical storms. • Collected measurements of ocean surface winds up to 72 m/s and rain rates over 100 mm/hr, and boundary layer winds in excess of 100 m/s. • Several flights coincident with WindSAT and QuikSCAT passes. • Hundreds of GPS drop-sondes deployed. • Collocated radiometer (SFMR) brightness temperatures measurements providing surface wind speed and precipitation estimates.

  6. Work performed • Obtained dual-polarized (H and V) C- and Ku-bandmodel functions of ocean backscatter versus wind speed and direction: • Wind speed > 25 m/s in rain-free conditions. • C-band H polarization (full range). • Compared against other models (CMOD4/5, NSCAT2, QSCAT1, etc.): • Shown a decreased sensitivity at high-winds. • Developed the model for the QuikSCAT incidence angles. • Implemented in a parallel NOAA/NESDIS/ORA NRT QuikSCAT 25-km and 12.5-km processor.

  7. log log High Winds Ku-band Model Function 25 25

  8. log log High Winds C-band Model Function

  9. Full-range C-band H pol. models

  10. A2/A0 versus wind speed C-band VV Ku-band VV C-band HH Ku-band HH

  11. C-band NRCS Azimuthal response HH49 deg VV50 deg

  12. Ku-band NRCS Azimuthal Response HH48 deg VV48 deg

  13. Conclusions • C- and Ku-band mean ocean backscatter measurements show a decreased sensitivity for wind speeds above ~45 m/s. • H-pol behaves similarly to V-pol for both C- and Ku-band at high wind speeds, but… • C-band H-pol at high incidence angles shows a much higher saturation point (not reached at 65 m/s). • C- and Ku-band A2/A0 measurements decrease to < 0.1 thus supporting the observed decreased sensitivity in wind direction as well. • Best bet to retrieve high winds (> 50 m/s) from scatterometry is C-band H-pol at high incidence angles.

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