GSICS Contribution to the Improvement of FY-2D/2E Operational Calibration Na Xu, Xiuqing Hu, Lin Chen, Min Min National Satellite Meteorology Center (NSMC)

OUTLINE Background Improvements in Operational Calibration Effects & Validation Conclusions & Lessons 对系统建立的背景及GSICS组织进行简单介绍 然后给出定标方法 最后针对定标结果进行检验分析 2

BACKGROUND FY-2 is a spin-scanning geostationary meteorological satellite. The onboard blackbody calibration facility for the IR bands cannot be used for absolute calibration, and is only a valuable tool for monitoring detector response . Inter-calibration method is used as the operational program for IR channels of FY-2C/2D/2E. Scenes radiance BB radiance

NOAA/AVHRR，NOAA/HIRS(WV) BACKGROUND Update of Operational Calibration MON Senor REF Sensor Time FY-2D/VISSR （86.5°E，from 2006/12） NOAA/AVHRR，NOAA/HIRS(WV) Launched - 2012/04 METOP-A/IASI 2012/04 - Now FY-2E/VISSR （105.5°E ，from 2008/12） Launched – 2012/01 2012/01- Now

Improvements in Operational Calibration GSICS inter-calibration algorithm based on METOP-A/IASI is adopted as operational program for FY-2D/2E infrared channels, since 2012-04 and 2012-01, separately. And calibration results are still delivered to data user in CAL LUT format. CAL Update Strategy : about once a week according to working conditions. Improvements to calibration algorithm ： Adjust collocation criteria：improve sample quality； Time sliding regression (just for Window and WV channels) ：insure the operational stability of calibration； Non-linear correction：improve calibration accuracy of cold scenes；

Improvements (1) — Adjust collocation criteria（temporal ,  spatial uniform） Observation time difference check | tFY2 − tsounder | < dtmax (10min) Environment uniformity check STDV(FY2 DN in ENV_BOX) < MaxSTDV MaxSTDV =8 count (TBB>=250K) （equivalent ~ 0.8k@290K） MaxSTDV =4 count (TBB<250K) （equivalent ~ 1.6k@200K ） Before：IR10.8μm After：IR10.8μm Sample correlation is improved, and noise is reduced

Improvements (1) — Enhance collocation criteria（dtmax , MaxSTDV ） IR12μm IR6.7μm Collocation samples of split window and water vapor channels (IR1~3) show excellent quality, and its correlation can reach to 0.99 or much higher. Due to stray-light contamination or solar reflective effects, collocation of medium infrared channel (IR4) shows relatively poor quality ,only correlation coefficient > 0.9 results are adopted. IR3.9μm 原来采用GSICS规范，先更严格，原因。。。。 散点图，线性度非常好

LUT Daily Variation: < 0.5K (TBB>220)， <1K (TBB<220) Improvements (2) — Time sliding regression LUT Daily Variation: < 0.5K (TBB>220)， <1K (TBB<220) Variation of calibrated TBB at specified counts (2010-11~2012-2) CAL coefficients for window or water vapor channels are calculated based on daytime collocation samples using 7 days sliding regression method CAL LUT is based on 7 days sliding regression of daytime collocation pixels

Improvements (3) — Non-linear Correction Non-linear Analysis —— FY-2D 10.8μm prelaunch vacuum measurements Measurements under different work conditions Cubic fitting method shows minimum errors ，that indicate non-linear feature appears during both strong and weak signal. Non-linear feature plays significant influence when observing cold targets. When TBB@~190K, linear fitting error is ~10K. Radiance error of different fitting methods TBB error of different fitting methods

Improvements (3) — Non-linear Correction Non-linear Analysis—— Collocation Samples FY-2D collocation fitting（low） Linearity of FY-2E is better than FY-2D FY-2E collocation fitting（low） 5K/Rad 0.5K/Rad Relationship between BB radiance and TBB 从观测样本反映非线性 Fy2e线性度好于FY2D

Effects & Validation— Calibration Bias FY-2 vs AQUA/AIRS Operational calibration of FY-2D/2E was upgraded using GSICS inter-calibration algorithm in 2012-04 and 2012-01 separately. The calibration biases were sharply decreased, and reduced to about 0.5~1K@290K (@250K）without eclipse period. Before upgrade, calibration bias of FY-2D was about 1~2K@290K in split window channels, and 3~4K@250K in WV channel. Tbb bias presents a significant cyclical fluctuation ,and reaches 4-6 K every September during the Autumn eclipse phase. Before upgrade, calibration bias of FY-2E was about 1~3K@290K in split window channels (IR2 is larger than IR1). TBB bias in WV channel@250K is similar large as FY-2D but without seasonal fluctuation. Eclipse Phase Time series of calibrated TBB bias for IR1~3 channels vs AQUA/AIRS reference scenes (290 K for IR1 and IR2, 250 K for IR3).

Effects & Validation— TBB_IR10.8um - TBB_IR12um Negative value 11% →3% The proportion of negative value is greatly reduced according to GSICS inter-calibration algorithm. 对于晴空区，两个通道亮温差是合理的，均为+值，说明多通道产品反演已经可用GSICS的FY2E定标表 TBB difference between split window channels (IR1-IR2) of FY-2E under clear sky condition—2011 Left ：PDF (solid line) and CDF (dashed line); Right：TBB Dif distribution varying with scenes temperature 12

Minmum TBB Comparison (IR1) FY2D Linear FY2E Linear FY2D Nonlinear FY2E Nonlinear MODIS MTSAT 04:15 04:32 04:25 04:30 2011.05.26 “Songda” Minmum TBB Comparison (IR1) Effects & Validation— Calibration for Cold Targets TBBmin DTBB MODIS 189.8 MTSAT 191.2 0.4 FY2E Linear 183.6 -6.2 FY2E Nonlinear 189.4 -0.4 FY2D Linear <180 > -9.8 FY2D Nonlinear 183.8 -6.0 10% TBBmin 195.6 198.4 2.8 190.2 -5.4 195.5 -0.1 < 187.2 > -8.4 190.8 -4.8 0.2°*0.2° projection Center position~125°E

Average of differences in Minimum TBB （Mean(|DTBBmin|)， K） Effects & Validation— Calibration under Cold Targets Average of differences in Minimum TBB （Mean(|DTBBmin|)， K） Three typhoon cases are selected in each spatial part. And the observation time is limited to that of AUQA overpass. Sensor comparison TBB Dif of West typhoon TBB Dif of East typhoon FY2E-MODIS 2.97768 0.7052 FY2D-MODIS 0.96934 4.0786 FY2E-FY2D 2.00834 3.3733 FY2D FY2E WEST EAST 阿拉伯海 孟加拉湾 西太平洋 Center position of Typhoon cases

Conclusions & Lessons GSICS inter-calibration using hyper-spectral reference instruments provides a good method for FY-2 operation calibration, and has improved 2D/2E operation calibration accuracy. GSICS is also an useful tool to monitoring FY-2/VISSR calibration bias trend in orbit and providing frequency information of instrument status. When inter-calibration is used as an operation program, quality control is great important, as excessive noisy in collocation will lead to instability of operational calibration. Non-linear correction is necessary for FY-2, and can improve the calibration accuracy especially in low radiance (temperature). Non-linear feature of FY-2 needs further investigation. Inter-calibration in medium infrared channel should be dealt with seriously. Time sliding regression method is not applicable and calibration calculation is better to be completed with nighttime collocation samples. 应用到FY-2对FY-2定标有明显提高； 质量控制很重要 非线性订正对低温段定标很重要；为了长期还需继续分析非线性特性 受。。。，对待午夜和中红外通道要区别对待。

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