1. GOCI: Early In-Orbit Performances
2011 IGARSS TH3.T05
GOCI: Early In-Orbit Performances
July 28, 2011 Vancouver, CANADA
Han-Dol KIM*, Gm-Sil Kang*, Joo-Hyung Ryu**
Pierre Coste†, Philippe Meyer †
*Korea Aerospace Research Institute (KARI)
**Korea Ocean Research and Development Institute (KORDI)
†EADS Astrium

2. Agenda Introduction of COMS Introduction of GOCI
Current Status of COMS and GOCI
GOCI In-Orbit Performances
Conclusion

3. Introduction of COMS (1)
COMS: Communication, Ocean and Meteorological Satellite
Geostationary satellite
Mass at Launch: 2460 kg
Orbital Location: 128.2oE
Design Life time: 10 years
Operational Life: 7.7 years
Launch: June 26, 2910, 21:41 (UTC)
Launcher: Ariane 5 ECA
COMS Missions
A meteo mission (MI)*
An ocean imager mission (GOCI)**
An experimental Ka band telecommunication mission
* MI: Meteorological Imager
** GOCI: Geostationary Ocean Color Imager

4. Introduction of COMS (2)
The main characteristics of COMS
- Operational lifetime: 7.7 years
- Design lifetime: 10 years
- Orbital position: 128.2°E
- Launch mass: 2460 Kg
- Payload mass: 316 Kg
- Payload power: 1077 W
- Power generation: 2396 W by GaAs cells solar array
- Pointing performance:
* better than +/- 0.05°absolute pointing error in roll and pitch for
MI/GOCI
* better than 0,11°(half cone) error for Ka band RF beam pointing
* pointing stability;
10µrad (N/S and E/W) peak to peak over 8s period
55µrad (N/S and E/W) peak to peak over 120s period

5. Introduction of GOCI (1)
Overview
world’s 1st geostationary ocean color imager, jointly developed by EADS Astrium and KARI
8 channels/spectral bands (6-Visible and 2-NIR)
provides multi-spectral data regarding coastal ocean environment for marine science research and application purpose
spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands (the ninth one for detector dark current measurement)
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.

6. Introduction of GOCI (2)
Performance requirement specification
Items
Technical requirements
Ground Sample Distance (GSD)
 500m  500m at the center of the target area
Target area
2500km  2500km
centered on (36N , 130E)
Spectral coverage
412 nm ~ 865 nm
(8 channels)
Bandwidth
10 nm ~ 40 nm
SNR
750 ~ 1200
System MTF
0.3 on all bands
(after ground processing)
Dynamic range
NEdR ~ Maximum cloud radiance
Radiometric calibration accuracy
4 %
Digitization
12 bit
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.

7. Introduction of GOCI (3)
Key Design Features (i)
(Z+ Earth)
Five Key Elements: Three mechanisms (SCM, FWM, POM), Telescope Assembly and FPA.
Functional chain, in the order of: SCM, POM, Telescope Assembly, FWM, FPA
Calibration mechanism: SD & Diffuser Aging Monitoring Device (DAMD), a smaller aperture diffuser using identical material to SD (QVD), to be used infrequently and suffer virtually no degradation due to contaminant buildup and polymerization from solar exposure, which allows maintaining the calibration accuracy.
GOCI Main Unit (w/o MLI protection)

8. Introduction of GOCI (4)
Key Design Features (ii)
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.
GOCI Main Unit (w/o MLI protection) during integration phase

9. Introduction of GOCI (5)
Key Design Features (iii)
- FPA (Focal Plane Assembly)
GOCI Detector & FEE (Front End Electronics)
2-D array, COMS detector: 1415(EW)x1432(NS) pixels
2 sub-arrays: 1415 x 715 pixels
2 lead-out channels for each sub-array
Low noise amplification of 4 lead-out channel signals of the detector by FEE
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.
GOCI CMOS Detector

10. Introduction of GOCI (5)
Key Design Features (vi)
- Telescope Assembly:
* Three Mirror Anastigmat (TMA) design, providing good MTF performance over the field of view on focal plane array, with all mirrors made of SiC to lower weights and minimize thermal effects
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.

11. Introduction of GOCI (5)
Key Design Features (v)
- FWM (Filter Wheel Mechanism)
* 1-D rotation, Filter Wheel
* 8 spectral filters
* 1 Dark plate for offset measurement
- POM (Pointing Mechanism)
* An High accuracy pointing assembly, used to select slot
positions
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.

12. Introduction of GOCI (6)
Key Design Features (vi)
- SCM (Shutter & Calibration Mechanism)
Shutter wheel (1-D rotation)
* For the earth view when opening and for closing instrument cavity when it is inactive
* SD (Solar Diffuser): for the sun view. effectively insensitive to radiation degradation over mission life time (made of Quasi Volumic Diffuser (QVD)).
* DAMD (Diffuser Aging Monitoring Device): for the sun view. a smaller aperture diffuser using identical material to SD, to be used infrequently and suffer virtually no degradation, which allows maintaining the calibration accuracy.
Spectral band selection is ensured by a 9-position filter wheel: 8 positions correspond to the 8 wavebands, and the ninth one is used for detector dark current measurement by providing a full occultation view.

13. Current Status of COMS & GOCI (1)
COMS launch and mission timeline

14. Current Status of COMS and GOCI (2)
COMS lOT Summary (July 2010~ Feb 2011)
Bus IOT
- All functional checks are completed and Bus is in
good health.
- Performance checks are completed and
subsystems are showing excellent performances.
Payload IOT
- All functional checks are completed and all three
payloads are in good health.
- Radiometric performance checks and radiometric
calibration have been completed.
- Geometric calibration has been completed with the
focus on INR tuning.

15. Current Status of COMS and GOCI (3)
GOCI Status Summary
Normal Operation for the service to the end user
has set forth at the completion of IOT (FAR),
from April 2011.
Current GOCI Status
- GOCI is in good health with all functions in good
check.
- Radiometric calibration is exhibiting good trace of
performance, calibration and stability.
- Geometric correction is exhibiting good landmark
matching and excellent INR performance metric.

16. GOCI In-Orbit Performances (1)
Functional chain architecture of Data Processing

17. GOCI In-Orbit Performances (2)
Radiometric Performances (1)
Radiance Response
GOCI radiometric model has been validated through ground test
S: Output (Digital count), L: Incident Radiance
G: Linear gain, b: Nonlinear gain, Tint: integration time
O: Dark current offset parameter, F: Fixed offset parameter
2D mapping parameter O
2D mapping parameter F
In orbit offset parameter  Ground offset parameter

18. GOCI In-Orbit Performances (3)
Radiometric Performances (2)
Radiance Response (ii)
GOCI radiometric model has been validated through ground test
Digital count image of Sun diffused by SD
Ground Measured Radiometric Response
In-orbit radiometric responsivity G & b , PRNU (Pixel Response Non-Uniformity)
 On-ground measured values

19. GOCI In-Orbit Performances (4)
Radiometric Performances (3)
Radiometric calibration and stability (i)
GOCI radiometric calibration using Sun light through Solar diffuser
 Covering whole imaging chain (telescope and video chain) for Earth
observation (SD is located in front of pointing mirror)
 Covering full pupil
 Monitoring of Solar diffuser aging using secondary solar diffuser
In orbit calibration method using two images has been verified through IOT duration.
SD image for
long integration time
SD image for short integration time
Gain matrix

20. GOCI In-Orbit Performances (5)
Radiometric Performances (4)
Radiometric calibration and stability (ii)
Gain matrix calculation
Linear
gain
Non-linear
gain
where Es : solar irradiance,
: sun images
: measurement parameter for sun imaging
SD: diffusion factor of SD, SD: solar incident angle, TSD: integration time
Using two measurement points SA, SB (two images)
: image with long integration time & image with short integration time
Using solar irradiance ES calculated from the solar spectrum model (Thuillier 2004) provided by GOCI user group
Using diffusion model SD of SD characterized on-ground
Using solar incident angle SD calculated from Ephemeris data and telemetry 20

21. GOCI In-Orbit Performances (6)
Radiometric Performances (5)
Radiometric calibration and stability (iii)
Radiance image calculation using in-orbit gain matrix
where : raw data after offset correction
: Gain parameters calculated through in-orbit solar calibration
08/09/2010, 00:15:00 UTC
L0 image
(raw digital image, slot 7, B8)
L1A image
(radiance image, slot 7, B8)

22. GOCI In-Orbit Performances (7)
Radiometric Performances (6)
Radiometric calibration and stability (iv)
Evolution of mean gain over 5 months: about 2% degradation
(Stabilization after 3 months)

23. GOCI In-Orbit Performances (8)
Radiometric Performances (7)
SNR
SNR has been assessed indirectly by using in orbit gain matrix.
IOT SNR measurement > Specification
Nominal side
Redundant side

24. GOCI In-Orbit Performances (9)
MTF
MTF has been assessed by KEF image for Band 7 and Ban 8.
IOT MTF measurement > Specification
Example of E/W MTF measurement (KEF)

25. GOCI In-Orbit Performances (10)
Geometric Performances (1)
GSD
GSD at FOV center has been assessed.
IOT GSD measurement: OK

26. GOCI In-Orbit Performances (11)
Geometric Performances (2)
Geometric Correction: INR
- A new, noble approach to INR system design
- Not directly dependent on system and/or payload
models and hence can avoid any indispensible
modeling and/or prediction error in the process
- Acquisition of sufficient number of landmarks in
good quality is key to this design
- Excellent landmark matching algorithm and the
fine-tuning of newly established landmark database
with ample landmark sites render such acquisition
of sufficient number of good landmarks

27. GOCI In-Orbit Performances (12)
Geometric Performances (3)
GOCI INR performances (i)
- Accuracy performances on landmarks have been checked
on KORDI GOCI operational platform (1FEB2011 to 7FEB2011)
- GOCI INR performances have been re-checked after the
final adjustment (15FEB2011 to 21FEB2011)

28. GOCI In-Orbit Performances (13)
Geometric Performances (4)
GOCI INR performances (ii)
Mean
Standard
Deviation
Performance
(mrad) EW NS
Navigation
0.05
0.46
0.56
0.52
1.72
2.03
24.1
28.4
Band-to-Band
Reg.
-0.01
0.00
0.30
0.25
0.92
0.74
12.9
10.4

29. GOCI In-Orbit Performances (14)
Geometric Performances (5)
GOCI INR performances (iii): Example of shoreline matching (B7)

30. GOCI In-Orbit Performances (14)
Geometric Performances (6)
GOCI INR performances (vi): Example of shoreline matching (B7)

31. GOCI Sample Images (1)

32. GOCI Sample Images (2)

33. GOCI Sample Images (3)

34. GOCI Sample Images (4)

35. Conclusion
The newly developed GOCI is demonstrating quite decent performances in orbit, both in radiometric and geometric aspects.
It is anticipated that such GOCI image data will bring a new dimension to the geostationary remote sensing and in the related scientific research fields.
More in-depth review, thorough analysis and active iteration are desired to define the requirement specification for the next generation GOCI (‘GOCI-2’).
It is hoped that GOCI will further be expanded in terms of its design, development, operation and applications, into the next generation of geostationary remote sensing satellites.