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

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

Comparison of Two Radiometers TMIAMSR-E Coverage40S-40NGlobal Orbitnon-sunsun-sym (1PM) DurationDec ~May 2002 ~ Freq. (GHz)10,19,21,37,856,10,18,23,36,89

Monitoring of El Nino and La Nina by AMSR-E

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

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 ºC error

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

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

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

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

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

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

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

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

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

Result of Error Estimation for AMSR-E 6V in Ascending Orbit Equ.60S60N Jan. Dec. 1K

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

AMSR-E SST Accuracy –Bias- (unit ºC) SST Range Jan. Apr. Jul. Oct. N.H. 0- 5ºC S.H

Long Term Trend of AMSR-E Tb

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