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Calibration Method of Microwave Tb for Retrieving Accurate SST Akira Shibata JAXA / EORC PowerPoint Presentation
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Calibration Method of Microwave Tb for Retrieving Accurate SST Akira Shibata JAXA / EORC

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Calibration Method of Microwave Tb for Retrieving Accurate SST Akira Shibata JAXA / EORC

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  1. Calibration Method of Microwave Tb for Retrieving Accurate SST Akira Shibata JAXA / EORC Advances of Satellite Oceanography at Vladivostok , Oct. 3-6, 2007

  2. Microwave SST • Microwave radiometers with lower frequencies (6-10GHz) can provide SST through clouds, which is very valuable both for operational and research works • Two radiometers, Advanced Microwave Scanning Radiometer–E (AMSR-E) and TRMM Microwave Imager (TMI), have been operated normally for five years and ten years, respectively • But, a calibration issue of brightness temperature (Tb) for both sensors still remains

  3. Comparison of Two Radiometers TMI AMSR-E Coverage 40S-40N Global Orbit non-sun sun-sym (1PM) Duration Dec. 1997 ~ May 2002 ~ Freq. (GHz) 10,19,21,37,85 6,10,18,23,36,89

  4. Monitoring of El Nino and La Nina by AMSR-E

  5. Monitoring of Positive SST Anomaly in Arctic Ocean by AMSR-E

  6. Tb Calibration Issue • Latest version (V3) of JAXA for AMSR-E still contains a calibration error of Tb with 1K order, and NASA V6 TMI also contains an error with similar order • Sensitivity of microwave Tb of 6V and 10V to SST is 0.5K/ºC for SST above 10 ºC, and its value of 6V around SST 0 ºC is 0.3K/ ºC • Therefore, Tb must be calibrated with an error of less than 0.1K to obtain accurate SST of 0.1-0.2 ºC error

  7. Microwave SST Algorithm Outline in case of AMSR-E 1. Atmospheric correction on 6V using 23V and 36V 2. Wind correction on 6V using 6H • dependable on relative wind direction, of which information can be estimated by a combination of 36GHz and 6H • also dependable on air-sea temperature difference, in which air temperature is obtained from a weather forecast model 3. Salinity correction on 6V 4. Convert 6V to SST 5. Remove following areas • sea ice, sun glitter, and coast

  8. Wind Correction on 6/10V (1/2) Δ 6/10V = 0 for 6/10H* less than z0 = (6/10H* – z0) × sp for 6/10H* greater than z0 6V*(K) slope=sp up cross down 6H*(K) z0

  9. Wind Correction on 6/10V (2/2) 6V(H)* = amsr_6V(H) – atmos_effect_6V(H) – calm_ocean_6V(H) SST dependent 10V(H)* defined similarly for TMI 10GHz

  10. Tuning of Tb (1/3) Calibration of 6/10V ; To minimize a difference of two SSTs in a range of 6/10H* between (z0-1) and z0 Calibration of 6/10H ; To minimize a jump of SST difference around z0

  11. Tuning of Tb (2/3) – 6/10V - Sensitivity of 6/10V to SST ~ 0.5K/ °C +0.2K -0.2K

  12. Tuning of Tb (3/3) – 6/10H - Impact of 6/10H on SST ~ 1K/ °C +0.2K -0.2K

  13. Result of Error Estimation for TMI 10V in case of Satellite Forward Direction in Apr.-May Day 10H error ~ 10V × 0.7

  14. Result of Error Estimation for TMI 10V in case of Satellite Backward Direction in Apr.-May Day

  15. After Tuning of Tb Local time TMI Jan.1, 2006

  16. Result of Error Estimation for AMSR-E 6V in Ascending Orbit Jan. 1K Dec. 60S Equ. 60N

  17. AMSR-E SST Accuracy -RMS- comparison with buoys during 5 years in Northern Hemisphere (N.H.) July January rms = 0.49ºC rms = 0.60ºC

  18. AMSR-E SST Accuracy –Bias- (unit ºC) SST Range Jan. Apr. Jul. Oct. N.H. 0- 5ºC 0.37 0.19 —— 5- 10 0.07 0.19 0.03 0.00 10-15 0.00 0.14 0.02 0.08 15-20 -0.03 0.03 -0.05 0.03 20-25 -0.08 0.05 -0.03 -0.03 25-30 -0.05 0.02 0.03 0.00 S.H. 25-30 -0.06 -0.09 -0.03 0.02 20-25 -0.09 -0.14 -0.12 -0.10 15-20 -0.01 -0.03 -0.08 -0.03 10-15 0.00 0.03 -0.07 -0.01 5-10 -0.08 -0.01 -0.05 0.11 0- 5 -0.25 -0.28 -0.05 0.06

  19. Long Term Trend of AMSR-E Tb

  20. Conclusions • Method of calibrating microwave Tb at 6 and 10GHz was presented, which was based on a wind correction on 6/10V • After tuning of TMI Tbs, a diurnal cycle of SST was clearly observed • After tuning of AMSR-E Tbs, a difference of AMSR-E and buoy SSTs was mostly laid within 0.1ºC, though 0.2 or 0.3 ºC difference was found in low SST in both hemispheres • Trend of AMSR-E Tbs was not observed, which might indicate an application for monitoring the global SST warming in a near future, by combining AMSR-E and its following