1. Lunar data preparation for FY-2
Lin Chen
National Meteorological Satellite Center
Acknowledgement:
Sébastien Wagner(EUMETSAT);Xi Shao(NOAA)
Scott Hu; Lu Zhang (CMA)
Nov. 13~16, 2017, Xi'an, China

2. Outline FY2/S-VISSR Intruduction
Answer to Questionnaire On Lunar Data Preparation
FY2E Lunar calibration results by GIRO Comparison with DCCs method

3. 1. FY2/S-VISSR Intruduction
Satellite
Launch Time
Application Status & Main Characteristics
FY-2A
1st subseries: experiment satellite
Main detection functions are validated
Partial kernel techniques are conquered
FY-2B
FY-2C
2nd subseries: operational satellite
Space & ground systems are steadily established
Primary quantitative applications are realized
FY-2D
FY-2E
FY-2F
3rd subseries: operational satellite
Straylight improment
FY2G

4. FY2/S-VISSR Sensor Specification
Spectral bands
5 bands including
1 VIS band and
4 IR bands
Resolution
1.25km for VIS
5km for IR
Earth scan angle
20°*20°
Scan sampling
10000 scan for VIS band
2500 scan for IR bands
Scan time
0.6s
Quantization
6bit for VIS(0~63)
10bit for IR(0~1064)
IFGOV
35urad for VIS
140urad for IR
There is a big improvement for FY2F VIS band. The SRF is more narrow and move to shorter wavelength with less absorption.
Four detectors of FY2F VIS band are Consistent
FY2 SRF:
FY2 MTF: to be presented in the coming 2nd workshop

5. FY2 VIS Band Calibration
No on-board calibrator
Vicarious calibration :
Deep Convective Clouds
Gobi desert on Dunhuang
Deep space
Quadratic responsivity correction
DN convert to Voltage(non-linear)
Voltage convert to radiance/reflectance(linear)

6. Answer to Questionnaire On Lunar Data Preparation
1. How is the Moon located in the image？
Moon acquisition
Free moon randomly transits across the FY2 Field of view
Manoeuver by sub-area scan scheme
Phase angle range
random by free moon( we can select -92o ~ 92o data for analysis)
according to the manoeuver scheme
FY2E and FY 2G Lunar L1alpha data in netCDF format available
To be provided to GLOD if approved by CMA

7. Free moon randomly transits across the FY2 Field of view

8. Manoeuver by sub-area scan scheme

9. 2.How is the extraction performed?
Principe：Using the IR band and image processing algorithom for extraction the moon from the full disk images:
(1) set DN>threshold to 0; DN<=threshold to 1;
(2) Find the maximum number of element(must be the earth),set to 0;
(3) Find the second maximum number of element(the moon), set the rest elements to 0;
(4) An imagette is set to 404 by 404 pixels

10. 3. At what level of processing is the image data extracted
Not the original native format. It is a format between native format and L1B.
For the free moon
oversampling correction has been done
alignment has not been done
For the manoeuver method
alignment has been done(moon motion
compensated)

11. Integration of all imagette pixels
4.How are the Moon pixels selected/integrated? 5. Calculation of the total irradiance
Integration of all imagette pixels
Substraction of the averaged space view counts plus all pixels
Ω: Sample solid angle
: calibrated each pixel radiance at (i,j) image coordinate
: calibrated space view radiance at (i,j) image coordinate

12. over-sampling consideration
a.How is the over-sampling determined? What is the actual value?
The over-sampling correction for FY2 lunar data have been done. So the value of over-sampling we set 1;
b.Does the over-sampling vary in time?
Yes. It vary from 1.27 ~ 1.33 for FY2 sensor for different pixels.
c.How is the pixel IFOV determined?
The IFOV is one of the instrument parameters that given by the manufacturer. And for FY2, it is a single detector.
Time
Measured Size
Physical Size
Oversampling
2015/02/05 05:21
4.71E-05
2015/02/05 06:00
4.67E-05

13. 6.Screening: what is the threshold for the distance from the Moon image to the Earth limb
Not considered yet.
The lunar extraction algorithm run automaticly and the lunar imagette contaminated by the earth scene will be removed manually.
Earth

14. 7. What is the deep space offset and dark signal level
7. What is the deep space offset and dark signal level? How is it determined?
We choose the 10 marginal lines of each sides for calculating the dark signals.

15. 8. Are there known issues with straylight or cross-talk?
For FY2E, there is heavy straylight effect and it is not homogenous which will great affect the results.
Due to the straylight restrained improvement of FY2G, the straylight effect is much lower than FY2E.
FY2G
FY2E
FY2E
FY2G

16. 9. How are the Moon imaging time and the spacecraft position determined?
Two Line Elements of Satellites
JPL ephemeris (DE421)
SGP4/SDP4
SPICE
Position of Satellite in ECI J2000 Frame
The parameters of instrument onboard Satellite
Position of lunar, Solar and Earth Satellite in ECI J2000 Frame
The lunar observations (time and position of satellite)

17. 3. FY2 Lunar calibration results by GIRO Comparison with DCCs method
Annual drift
Total drift
Moon
1.96%
9.2%
DCC
1.72%
8.1%
Linear fitting regression(f) is used here to get the instrument degradation

18. Thanks