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

2. 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

3. 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

4. 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 /04
METOP-A/IASI
2012/04 - Now
FY-2E/VISSR
（105.5°E ，from 2008/12）
Launched – 2012/01
2012/01- Now

5. 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 and , 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；

6. 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 ~
MaxSTDV =4 count (TBB<250K)
（equivalent ~ ）
Before：IR10.8μm
After：IR10.8μm
Sample correlation is improved, and noise is reduced

7. 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

8. 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 ( ~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

9. 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 linear fitting error is ~10K.
Radiance error of different fitting methods
TBB error of different fitting methods

10. 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

11. Effects & Validation— Calibration Bias
FY-2 vs AQUA/AIRS
Operational calibration of FY-2D/2E was upgraded using GSICS inter-calibration algorithm in and separately. The calibration biases were sharply decreased, and reduced to about eclipse period.
Before upgrade, calibration bias of FY-2D was about in split window channels, and 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 in split window channels (IR2 is larger than IR1). TBB bias in WV 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).

12. 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

13. Minmum TBB Comparison (IR1)
FY2D Linear
FY2E Linear
FY2D Nonlinear
FY2E Nonlinear
MODIS
MTSAT
04:15
04:32
04:25
04:30
“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

14. 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
0.7052
FY2D-MODIS
4.0786
FY2E-FY2D
3.3733
FY2D
FY2E
WEST
EAST
阿拉伯海
孟加拉湾
西太平洋
Center position of Typhoon cases

15. 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。

16. Thanks for your attention