Lunar Calibration Inter-Comparisonof SGLI, MODIS and VIIRSTomoyuki Urabea, Xiaoxiong Xiongb, Taichiro Hashiguchic, Shigemasa Andoa,
Yoshihiko Okamuraa, Kazuhiro Tanakaa and Masaaki Mokunoa
aJAXA
bNASA GSFC
cRESTEC

Acknowledgement• This work was supported by Jack of NASA/GSFC during my stay as a visiting
researcher last year.
• I'd like to acknowledge Taichiro Hashiguchi of RESTEC (Remote Sensing Technology
Center of Japan) for his efforts to obtain SGLI lunar calibration results.
• We'd like to thank USGS for developing and improving the ROLO model andEUMETSAT for implementing GIRO.

Contents
1.

2.

3.

4.

Introduction• Motivation of this study• GCOM-C/SGLI Overview and Specification• Bands and Lunar Phase Angles of SGLI, MODIS and VIIRSMethodology• SGLI Lunar Observation Method• SGLI Lunar Analysis Method

Results• Time Series of Measured Irradiance(SGLI)/Model Irradiance(GIRO)• Comparison of SGLI, MODIS and VIIRS over WavelengthDiscussion• Phase angle dependency

1. Introduction

-Motivation of this study• Lunar calibration• make it possible to compare radiometric performance of multiple remote sensing
satellite instruments on orbit• The methodology was developed by the NASA OBPG CVT and the NASA MCST for
SeaWiFS and MODIS and the technique has been applied to other satelliteinstruments• Lunar model• ROLO (Robotic Lunar Observatory) model of USGS
• GIRO (GSICS Implementation of the ROLO) was developed by EUMETSAT in 2014 andprovided access to the function of the ROLO lunar calibration model for theinternational community• In this paper, the lunar inter-comparison methodology and GIRO model for onorbit radiometric instrument are extended to include the GCOM-C/SGLI
observations.

-GCOM-C / SGLI Overview• GCOM-C (Global Change Observation Mission – Climate)• launched into a 798-km sun-synchronous polar orbit with a node of 10:30am on Dec. 2017
• SGLI (Second generation Global Imager)• VNR (Visible and Near-Infrared Radiometer) and IRS (Infrared Scanner)• optical sensors capable of multi-channel observation at wavelengths from near-UV to the thermal
infrared wavelength. (380nm to 12µm)• Images acquired by SGLI on GCOM-CVegetation
distribution of Japan

Namibia coastand desert

Coral reefs inthe Bahamas

Morning glow ofKamchatka peninsula

-SGLI Specification• The SGLI features are 250m spatial resolution for VNR-NP, SWI(B3) and TIR and polarization/ alongtrack slant view channels (VNR-PL), which will improve land, coastal, and aerosol observations.
SGLI channels
λCH

VN1
VN2
VN3
VN4
VN5
VN6
VN7VN8VN9VN10
VN11
P1P2
SW1
SW2
SW3
SW4T1
T2

∆λLstdLmax

VNR-NP, VNR-PL,
IRS-SWI: nm
IRS-TIR: µm

VNR-NP, VNR-PL,IRS-SWI:W/m2/sr/µm
IRS-TIR: Kelvin

380
412
443
490
530
565
673.5
673.5
763
868.5
868.5
673.5
868.5
1050
1380
1630
2210
10.8
12.0

60
75
64
53
4133
2325408302530
57
8
3
1.9
300
300

1010
101020202020
1220202020
2020
200
50
0.7
0.7

210
250
400
120
350
90
62
210
350
30
300
250
300
248
103
50
20340
340

SNR at Lstd

IFOV

VNR-NP, VNR-PL,
IRS-SWI : SNR
IRS-TIR: NE∆Tm

250
400
300
400
250
400
400
250
1200
400
200
250
250
500
150
57
211
0.2
0.2

250
250
250
250
250
250
250
250
250/1000
2502501000
1000
100010002501000
250/1000
250/1000

250m over
the Landor coastal
area, and1km overoffshore
Multi-angle
obs. for673.5nmand868.5nm

GCOM-C SGLI characteristics
Instruments
VNR (Push-broom electric scan)
IRS (Wisk-broom mechanical scan)(Scan)
1150km cross track (VNR-NP & VNR-PL)
Scan width
1400km cross track (IRS-SWI & IRS-TIR)
Polarization
3 polarization angles for VNR-PL
Nadir for VNR-NP, IRS-SWI and IRS-TIR,
Along track+45 deg and -45 deg for VNR-PL
direction
VNR-NP, VNR-PL: Solar diffuser, LED,Lunar cal. maneuvers, and dark current
by masked pixels and nighttime obs.
On-board
calibration

Digitalization
Mission Life

IRS-SWI: Solar diffuser, LED, Lunar, anddark current by deep space window
IRS-TIR: Black body and dark current by
deep space window
12bit
5 years7

-Bands and lunar phase angle of SGLI, MODIS and VIIRS• The current inter-comparison includes several bands of SGLI, MODIS and VIIRS as shown in the figure• Lunar observation condition of each instrument is shown in the tableLunar Phase angle and Observation PeriodLunar
Phase angle

Comparison Bands

GCOM-CSGLI-VNR+7±3 or-7±3 deg

AquaMODIS-55.5±1deg

SNPP
VIIRS

-51±1deg

Period of comparison(Number of Observation)
Jan. 31, 2018Dec. 23, 2018
(20 times)
Dec. 30, 2017Nov. 20, 2018
(12 times)
Dec. 30, 2017Nov. 20, 2018
(8 times)2. Methodology

-SGLI Lunar Observation Method• SGLI lunar observation method is introduced as an example.
• SGLI-VNR observes the Moon once a month through its
nadir view, which requires a spacecraft pitch maneuver, sothat the Moon is viewed in the same optical path.

MoonEarth
Lunar
Observation

Maneuver• The pitch rate across the Moon is slower than the scanning rate across the Earth,resulting in an oversampled image of the Moon.

Captured lunar
images of VNRNP 11 bands

Lunar digital
numberresponse ofVN11 obtainedby one pitch
maneuver10

-SGLI Lunar Analysis Method• Lunar data analysis methodologies of SGLI consists of 4 steps.
Step1

The lunar radiance is obtained by the following
equation,
1𝐿𝐿𝑘𝑘,𝑝𝑝 = 𝐺𝐺𝑘𝑘,𝑝𝑝 �� 𝐷𝐷𝐷𝐷𝑅𝑅𝑅𝑅𝑅𝑅 − 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷∆𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠,𝑘𝑘𝐿𝐿𝑘𝑘,𝑝𝑝 : 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟(𝑘𝑘 = 𝑐𝑐𝑐𝑐~11, 𝑝𝑝 = 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝)
𝐺𝐺𝑘𝑘,𝑝𝑝 : 𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚∆𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠,𝑘𝑘 : 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐
𝐷𝐷𝐷𝐷𝑅𝑅𝑅𝑅𝑅𝑅 : 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 (4 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 − 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝐶𝐶𝐶𝐶𝐶𝐶 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 × 4 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙)
𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 : 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑜𝑜𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 𝑜𝑜𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑜𝑜𝑜𝑜𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑎𝑎𝑎𝑎 𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝

Step3

Simulate lunar irradiance by GIRO model to normalize
the lunar calibration time series for variations inobserving geometry:• Spacecraft/Moon distances,• Sun/Moon distances,• phase and• libration angles

NP:500 line
PL:125line

Step2

The lunar irradiance is calculated by thefollowing equation,
𝐼𝐼𝑘𝑘 =𝑁𝑁� 𝛺𝛺𝑘𝑘,𝑝𝑝 𝐿𝐿𝑘𝑘,𝑝𝑝 �1
� sin 𝜃𝜃𝑓𝑓𝑜𝑜𝑜𝑜

𝑝𝑝=1
𝐼𝐼𝑘𝑘 : 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖(𝑘𝑘 = 𝑐𝑐𝑐𝑐~11)
𝑁𝑁: 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛 𝑜𝑜𝑜𝑜 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
𝛺𝛺𝑘𝑘,𝑝𝑝 : 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑝𝑝𝑝𝑝𝑝𝑝 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
𝑓𝑓𝑜𝑜𝑜𝑜 : 𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝜃𝜃: 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 − 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 𝑎𝑎𝑎𝑎𝑎𝑎 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠
𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎

Step4

Evaluate SGLI Measured Irradiancecompared to the GIRO Irradianceshown as follows,
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑅𝑅𝑅𝑅𝑅𝑅

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 = I𝑘𝑘𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 �I𝑘𝑘

Deep Space

NP:400 line
PL:100line

Integrated
Area*
NP:160 pixel
PL: 30pixel

Deep Space
NP:500 line
PL:125line

113. Results

-Time Series of Measured(SGLI)/Model(GIRO)-

Normalizedby first obs.

••

A time series of measured responses of VN1–11 normalized to the GIRO model are shown in the figure to the left. As wellknown, absolute spectral accuracy varies from 3 to 11% when compared measured value to model value.
Then, they are normalized by the value of February 1st, the results are shown in the figure to the right.
• Degradations of the telescope at short wavelengths (from 380nm to 565nm) are clearly observed as expected.
13• No degradations of the telescope at long wavelengths are observed.

-Comparison of SGLI, MODIS and VIIRS over Wavelength (1/2)SGLI/GIRO

MODIS/GIRO

VIIRS/GIRO

BandAve.

Std

BandAve.

Std

BandAve.

Std

VN1

1.093

±0.008------

VN2

1.091±0.008B81.117±0.007

M1

1.151

±0.003VN3

1.068±0.008B91.095±0.005M2

1.085±0.002

---

B3

1.089

±0.006---VN4

1.084±0.008

B10

1.092±0.005

M31.121±0.003

VN5

1.092±0.006

B111.062±0.005

-

-

-

VN6

1.068±0.006

B12

1.077

±0.006B4

1.057±0.006M4

1.098±0.005

-

-

-

B1

1.057

±0.007

-

-

-

VN7

1.058

±0.004B13

1.064±0.006

VN8

1.065

±0.003B14

1.071±0.006M5

1.101±0.005

VN9

1.073

±0.004

-

-

-

M6

1.110±0.005

VN10

1.028±0.004

VN11

1.040

±0.004B2

1.101±0.006

M71.114±0.004---B17

1.143±0.005---• The results of the inter-comparison over wavelengths are shown in this table and in this figure• They are averages and standard deviations of time-series of measured irradiance to the GIRO model for
SGLI, MODIS and VIIRS over the period of one year, respectively

-Comparison of SGLI, MODIS and VIIRS over Wavelength (2/2)• The relative biases and uncertainty between theinstruments are derived and reported in the table.
SGLI/MODIS MODIS/VIIRSVIIRS/SGLI

Bias(min. Band)

0.6%

0.9%

1.6%

Bias(max. Band)

6.6%

3.7%

7.7%

Uncertainty

3.8%

2.7%

3.4%

𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝑠𝑠𝑠𝑠𝑠𝑠 1)

�𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺)• The biases are derived by 1 − 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝑠𝑠𝑠𝑠𝑠𝑠 2)

�𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺)• The sources of uncertainty in these comparisons are Standard deviation of one-year
observations(<1%)
 Associated with prelaunch characterization ofSGLI (2.89%), and estimated by the on-orbit
calibration of MODIS (2%) and VIIRS (1.3%)
 The capability for in-band comparisons of lunar
irradiance measurements in the ROLO
model(1%)• There are slightly larger biases between
SGLI and other instruments

4. Discussion

•The libration angles for the selenographic
longitude and latitude of the spacecraft and theSun are shown (Upper right)
The phase angle time series at each lunar
calibration is shown (Lower right)-Phase Angle Dependency (1/2)••

Fits to Lunar Calibration Time Series

The residuals of the fits are shown (Center)

Residuals

SGLI(VN1-6)

Weakcorrelation between• A time seriesof measured
Residualsand Libration
responses ofVN1-VN6(SGLI/GIRO)
normalized to the GIRO
model are shown in thefigure on the upper left,
and the lunar time series
are fit by exponentialfunctions of time.

SGLI(VN7-11)• In the same manner, a timeseries of measured
response of VN7-VN11
normalized to the GIRO
model are shown in thefigure on thelower
left, andStrong
correlation
betweenResiduals
Phase
the lunar timeseriesandarefit angle
by constant(SGLI/GIRO)
value of time.

Libration vs Phase angle

17

-Phase Angle Dependency (2/2)• While the ROLO model provides wavelength-dependent phase angles correction for the SGLI
lunar time series, the observation may have another slight residual phase angle effect.
ROLO model

ROLO model vs PLEIADES observation•Hugh H. Kieffer and Thomas C. Stone, “Thespectral irradiance of the moon,” The
Astronomical Journal, 129:2887-2901, 2005

•ROLO's lunar empirical model of irradiance has beendeveloped that treats phase and libration.
The magnitude of the phase angle effects are ten to
twenty times greater than other effects includinglibration.

The residual phase angle dependence of theROLO model has been also described in
PLEIADES lunar observations.

S. Lachérade, O. Aznay, B. Fougnie, L. Lebègue, “POLO: a unique dataset to derive the phase angle dependence ofthe Moon irradiance,” Proc. SPIE 9241, Sensors, Systems, and Next-Generation Satellites XVIII, 924112 (7 October2014); doi: 10.1117/12.2067283

-Comparison of SGLI/SeaWiFS and MODIS/VIIRS over Wavelength+ SeaWiFS (Phase angle = ＋7 deg.)• In addition, we found that SeaWiFS, whichobserved the moon at phase angle of 7 deg., hassimilar shape over wavelength with SGLI.
• There are slightly larger biases between
SGLI/SeaWiFS and MODIS/VIIRS• It is likely to be caused by the difference inthe lunar phase angles (7deg. vs -51~-55deg)• About 3-5% residual phase angle dependence in
the ROLO model has been observed with many
instruments such as MODIS, SeaWiFS andPLEIADES.

R. E. Eplee, Jr., J.-Q. Sun, G. Meister, F.S. Patt, X. Xiong, and C.R. McClain, “Cross calibration of SeaWiFSand MODIS using on-orbit observations of the moon,” Appl. Opt. 50, 120–133 (2011).

• Therefore, the results are reasonable and the SGLI
radiometric response relative to the GIRO model
are in family with those observed by the heritage
instruments.

5. Conclusion• Lunar inter-comparison methodology and GIRO model for on-orbit radiometric
instrument are extended to include the GCOM-C/SGLI observations.

• The current inter-comparison includes several bands of SGLI, MODIS and VIIRS fromthe near-UV (380nm) to the near-infrared wavelength(868nm).
• Time Series of Measured(SGLI)/Model(GIRO) are analyzed and degradations of thetelescope at short wavelengths (from 380nm to 565nm) are clearly observed asexpected.
• The residual of phase angle dependence of the ROLO model has been observed inSGLI lunar observations like other instruments.

• As for inter-comparison over wavelength, the results are reasonable and the SGLI
radiometric response relative to the GIRO model are in family with those observed by
the heritage instruments such as MODIS and VIIRS.

Data Release to public from Dec. 2018https://gportal.jaxa.jp/Vegetation distribution of JapanCoral reefs in the Bahamas

Namibia coast and desert

Morning glow of Kamchatka
peninsula

SGLI scientific products had been released to public on Dec. 2018 via JAXA’s data distribution system, GPortal.
• Level 1 products• Level 2 and 3 products (more than 28 scientific products including clouds, aerosols, ocean color,vegetation, snow and ice, and other applications.)