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MetOp-A AMSU-A Scan Asymmetry Characterization

MetOp-A AMSU-A Scan Asymmetry Characterization. Huan Meng, Ralph Ferraro STAR/CoRP/SCSB Acknowledgement: Wanchun Chen, Ninghai Sun. Problem. Along scan line asymmetry is observed in AMSU-A window channels from NOAA-15, -16, -17, and -18. The asymmetry impacts products quality

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MetOp-A AMSU-A Scan Asymmetry Characterization

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  1. MetOp-A AMSU-A Scan Asymmetry Characterization Huan Meng, Ralph Ferraro STAR/CoRP/SCSB Acknowledgement: Wanchun Chen, Ninghai Sun

  2. Problem • Along scan line asymmetry is observed in AMSU-A window channels from NOAA-15, -16, -17, and -18. • The asymmetry impacts products quality • MetOp-A AMSU-A measurements also exhibit asymmetry and need correction

  3. Correction Approach • Simulate Tb’s of 4 window channels (23.8, 31.4, 50.3 and 89 GHz) with radiative transfer model • Over ocean and clear sky • Input data from GDAS: SST, surface wind, and temperature and moisture profiles. • Derive the average difference between simulated and observed Tb at each beam position. • Need enough data (30+ days) to smooth out the effect of weather processes.

  4. AscendingTb Bias(~7days, 21438 points)

  5. Descending Tb Bias(~7days, 22995 points)

  6. Tb correction equation Tbo: observed Tb  : local zenith angle : asymmetry correction coefficients

  7. Before Asymmetry Correction After Asymmetry Correction

  8. Before Asymmetry Correction After Asymmetry Correction

  9. Synchronization of AMSU-A & MHS • DT ranges between -3 s to 8 s with MetOp-A. • DT = 0 with NOAA-15, -16 and -17. • DT = -5 s with NOAA-18

  10. Backup – NOAA-18 Asc

  11. Backup – NOAA-18 Des

  12. Backup – NOAA-15 Asc

  13. Backup – NOAA-15 Des

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