1. Calibration Activities of GCOM-W/AMSR2
Marehito KASAHARA
Earth Observation Research Center (EORC)
Japan Aerospace Exploration Agency
29 February 2016
2016 GSICS Data & Research Working Group Meeting
Tsukuba Space Center

2. GCOM-W Mission History
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
GCOM-W Mission History
GCOM-W launched by H-ⅡA launch vehicle
GCOM-W inserted into a planned position on the A-Train orbit
Started AMSR2 observation
Level-1 products released to the public
Level-2 products released to the public
All the products updated (Version2) 2

3. Overview of GCOM-W GCOM-W orbit Identical to that of Aqua
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Overview of GCOM-W
GCOM-W
Orbit
Sun synchronous sub-recurrent orbit
Recurrence cycle
16 days
Altitude
700 km
Inclination
98.2 deg
Local sun time of
descending node
1:30
mass
<1,991kg
power
> 3,880W
Design life
5 years
GCOM-W orbit
Identical to that of Aqua
Joining Afternoon constellation
Located in front of Aqua
(AMSR-E)
(AMSR2)
AMSR2 Control Unit (CU)
AMSR2
Sensor Unit (SU)

4. Overview of AMSR2 AMSR2 Characteristics Scan Geometry Scan type
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Overview of AMSR2
AMSR2 Characteristics
Scan type
Conical scan
Swath width
>1450 km
Antenna
Offset parabolic antenna
with deployment mechanism
2-meter-diameter aperture
Incidence angle
55 degree
Dynamic range
2.7K-340K
Center frequency
[GHz]
NEDT
[K]
Beam width [degree]
(Ground resolution [km])
6.925 / 7.3
< 0.34/0.43
1.8(35 x 62)
10.65
< 0.70
1.2(24 x 42)
18.7
0.65(14 x 22)
23.8
< 0.60
0.75(15 x 26)
36.5
0.35(7 x 12)
89.0 A/B
< 1.20/1.40
0.15(3 x 5)
Scan Geometry

5. Overview of AMSR2 AMSR2 Sensor Unit Configuration Stowed Deployed
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Overview of AMSR2
AMSR2 Sensor Unit Configuration
Rotating part
Feed-horn Array
Cold Sky Mirror
(CSM)
High-Temperature Noise Source
(HTS)
Main Reflector
Stationary part
calibration target
Feed-horn Array
Stowed
Deployed

6. Overview of AMSR2 Field of View (FOV) FOV of Main Reflector (Rotating)
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Overview of AMSR2
Field of View (FOV)
FOV of Main Reflector
(Rotating)
FOV of CSM
(Fixed)
Cold Calibration Target
(Cold Space)
Earth Observation Target

7. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Flow of radiometric calibration

8. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
CSM Data Correction

9. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
CSM (Lunar intrusion)
Global CSM data with lunar intrusion (36 GHz V)
After removal
Raw data
Corrected data
Path 185A

10. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
CSM (RFI)
Contaminated samples are detected, removed and linearly interpolated.
Detected RFI
Contaminated with RFI
7.3 GHz V-pol.

11. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
CSM (Earth radiation)
Earth radiation comes into CSM backlobe (spillover) from MREF.
CSM data(6.9 GHz H)
Increase of Antenna Temperature
ΔTc[K] = α×Tb[K]－β
Frequency
Pol. α β
6.9 GHz
V/H
0.2%-0.3%
0.04 K-0.06 K
7.3 GHz
10, 18, 23, 36, 89GHｚ
N/A

12. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
HTS Data Correction

13. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
HTS
Effective brightness temperature TH
TH = Tave - ΔThts
Tave ：physical temperature of HTS derived by averaging 10 measured temperature.
ΔThts:Bias due to an effect of deep space
Average among 10 measurements
Gap
3D analytical model for an effect of reflection

14. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Non-linearity and Scanbias Correction

15. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Non-linearity correction
Non-linearity is corrected based on pre-launch measurements.
Correction of lower frequency is relatively large (~5K).
Correction curve
amount of detector non-linearity correction (corrected TA)－(linearly calibrated TA)
at a temperature of 5℃
Measured data (6.9GHz H-pol.)
quadratic approximation of non-linear relationship between detector input power and detector output voltage from measurements

16. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
TA’ = TA×Cg(i) + C0(i)
Scan bias correction (Ocean/Land)
raw data TA
corrected data TA’
6.9G
7.3G
10G

17. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Conversion from Ta
to Tb

18. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Conversion from TA to TB
:Cross-polarization ratio
:Spillover ratio

19. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Spillover and Wide-angle sidelobe (Deep space)
Wide-angle sidelobe
Earth
Deep Space
STR
MREF
Deep Space
Center of MREF beam
Spillover
Edge of the Earth
Antenna pattern of feedhorn (6.9 GHz)
Antenna pattern of main reflector
(6.9 GHz)

20. Radiometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Radiometric calibration
Summary of radiometric calibration
Item
Amount of correction
Note
Cold calibration target
(CSM)
< 1.2K
an effect of the earth radiation from main reflector (< 0.35%) added to TC
not including occasional RFI and lunar intrusion removal
Hot calibration target
(HTS)
< 2.3 K
an effect of reflection (< 0.8%) subtracted from simple mean temperature value for TH
not including occasional low-frequency RFI removal
Input-output characteristic
(Detector non-linearity)
< 5 K
maximum at approximately 150 K
large in 7-GHz bands compared to the other bands
Scan bias
(Scan non-uniformity)
< 17 K
proportional to antenna temperature (< 5%)
only in scan edge of 7-GHz and 10-GHz bands
Spillover
（Cosmic background）
< 11 K
proportional to antenna temperature (< 3.3% including an effect of cosmic background from wide-angle sidelobe of MREF)
Cross-polarization
< 1 K
proportional to difference between TA of H-pol. and TA of V-pol.
Antenna loss
N/A
radiation from MREF and CSM surface (emissivity < 0.25% )
error in antenna temperature due to the antenna loss < 0.17 K (assuming that the surface characteristics of CSM is identical to that of MREF)
Random Noise
NEΔT, ΔG/G, 1/f noise
circuit noise, quantization noise

21. Mitigation of RFI Influence
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Mitigation of RFI Influence
RFI Mitigation
AMSR-E/AMSR2
RFI-contaminated data removed
6.9GHz V-pol. TB
merged
AMSR2
6.9GHz and 7.3GHz
AMSR2
RFI-contaminated data removed
7.3GHz V-pol. TB
merged

22. Geometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Geometric calibration
Summary of geometric calibration
Geolocation parameters were revised based on image matching between observed Tb data and coastline database.
offnadir angle
AMSR2 SU alignment angle (Roll, Pitch, and Yaw)
relative registration coefficients between 89 GHz A-channel and other frequency channels.
Geometric error (RMSE) of each channel is within the half of each spatial resolution.
Elevation
Azimuth
Along Track
Footprint
Scan Direction
Frequency
[GHz]
Spatial
Resolution
Geometric Error
Ver2.0 (RMSE) EL Az
6.9
　　62km
　　35km
　　6.3km
　　3.3km
7.3
62km
35km
5.9km
3.5km 10
41km
24km
3.6km
2.5km 18
22km
14km
2.0km
1.4km 23
26km
15km
1.5km 36
12km
7km
1.3km 89
5km
3km
0.9km
1.0km

23. Geometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Geometric calibration
Geometric error (89 GHz A-Scan)
Azimuth direction
Error(Pixel)
RMSE: pixel (1[pixel] = 4.5[km])
Sample number

24. Geometric calibration
2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Geometric calibration
Improvement of geodetic accuracy
Previous version　(Version1)
Current version
(Version2)
Tb difference between ascending and descending due to geometric error
Tb difference between ascending and descending (36GHz H-pol.)

25. 2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Future Work
Continue calibration activities.
Cause analysis of positive bias found out in the results of inter-comparison.
Feedback lessons learned to coming follow-on instruments.

26. 2016 GSICS Data & Research Working Group Meeting Tsukuba Space Center
Thank you