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Comparison of Wind Direction Retrieval Methods for SST Algorithm

This study compares the accuracy of two methods for retrieving relative wind direction used in the AMSR-E SST algorithm: 6H*/s36 versus 3/4th plane. The impact of wind direction on SST accuracy is analyzed, and the SSTs obtained from the two methods are compared. The study also examines the increase in WindSat SST areas compared to AMSR-E SST areas. The results show a relatively good correspondence between the two methods of wind direction retrieval, with the first method yielding better SST accuracy.

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Comparison of Wind Direction Retrieval Methods for SST Algorithm

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  1. Comparison of relative wind directions retrieved from AMSR-E method and from WindSat polarimetric method Akira Shibata Meteorological Research Institute AMSR-E meeting, at Telluride, July 14-16, 2008

  2. Study Purposes • Validate a method of retrieving a relative wind direction used in the AMSR-E SST algorithm, by comparing it with the polarimetric data of WindSat. • Compare the accuracy of SST obtained from two methods of retrieving the relative wind direction. • Compose two images of AMSR-E and WindSat SST

  3. Impact of relative wind direction on SST accuracy – 6V*/ 6H* plane - (K) slope=sp cross up 6V* Δ6V= 0 6H* < z0 = (6H* – z0) × sp 6H* > z0 down z0 6H* (K) SST accuracy Constant sp rms= 0.629℃ Varying sp rms= 0.601℃ in Feb. 2003

  4. Method of retrieving relative wind direction used in AMSR-E SST algorithm - 6H* / s36 plane - cross (K) 16m/s up down 6H* 7m/s (K) s36 s36 = (36H - (a × (36V – b) + c ) ) / atmos_corr

  5. Method of retrieving relative wind direction using WindSat 3/4th channel 18GHz Lyzenga (Nov. 2004)

  6. Comparison of two methods at 6H*=6K (7.7m/s) F U up cross down from 6H*/s36

  7. Comparison of two methods at 6H*=9K (11.7m/s) up cross down from 6H*/s36

  8. Comparison of two methods at 6H*=12K (15.0m/s) up cross down from 6H*/s36

  9. Comparison of SST accuracy obtained from two methods in Apr. 2003 6H*/s36 3/4th Total 0.68 ℃ 0.73 ℃

  10. WindSat SST on Apr. 1, 2003

  11. AMSR-E SST on Apr. 1, 2003

  12. AMSR-E + WindSat SST on Apr. 1, 2003 6% increase

  13. AMSR-E + WindSat SST on Apr. 2, 2003 11% increase

  14. Average percentage of area increments 10 % during 16days Repeat cycle AMSR-E 16days WindSat 29days

  15. Conclusions • Two methods of retrieving the relative wind direction were compared: 6H*/s36 versus 3/4thplane, and a relatively good correspondence was obtained. • Two SSTs obtained from two methods were compared, and the SST accuracy from the first method was better than the second one, which may be due to a narrow distance between cross- and up- directions in 3/4th plane. • WindSat SST increase 10% areas of AMSR-E SST.

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