Lunar Calibration Inter-Comparisonof SGLI, MODIS and VIIRS

Tomoyuki Urabea, Xiaoxiong Xiongb, Taichiro Hashiguchic, Shigemasa Andoa, Yoshihiko Okamuraa, Kazuhiro Tanakaa and Masaaki Mokunoa

aJAXAbNASA 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 and EUMETSAT for implementing GIRO.

Contents

1. Introduction• Motivation of this study• GCOM-C/SGLI Overview and Specification• Bands and Lunar Phase Angles of SGLI, MODIS and VIIRS

2. Methodology • SGLI Lunar Observation Method• SGLI Lunar Analysis Method

3. Results• Time Series of Measured Irradiance(SGLI)/Model Irradiance(GIRO)• Comparison of SGLI, MODIS and VIIRS over Wavelength

4. Discussion• 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 satellite instruments

• Lunar model• ROLO (Robotic Lunar Observatory) model of USGS• GIRO (GSICS Implementation of the ROLO) was developed by EUMETSAT in 2014 and

provided access to the function of the ROLO lunar calibration model for the international community

• In this paper, the lunar inter-comparison methodology and GIRO model for on-orbit radiometric instrument are extended to include the GCOM-C/SGLI observations.

Vegetation distribution of Japan

Namibia coast and desert

Morning glow of Kamchatka peninsula

• 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-C

Coral reefs in the Bahamas

-GCOM-C / SGLI Overview-

7

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

GCOM-C SGLI characteristicsInstruments(Scan)

VNR (Push-broom electric scan)IRS (Wisk-broom mechanical scan)

Scan width 1150km cross track (VNR-NP & VNR-PL)1400km cross track (IRS-SWI & IRS-TIR)

Polarization 3 polarization angles for VNR-PLAlong track direction

Nadir for VNR-NP, IRS-SWI and IRS-TIR, +45 deg and -45 deg for VNR-PL

On-board calibration

VNR-NP, VNR-PL: Solar diffuser, LED, Lunar cal. maneuvers, and dark current by masked pixels and nighttime obs.

IRS-SWI: Solar diffuser, LED, Lunar, and dark current by deep space window

IRS-TIR: Black body and dark current by deep space window

Digitalization 12bitMission Life 5 years

SGLI channels

CH

λ ∆λ Lstd Lmax SNR at Lstd IFOV

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

VNR-NP, VNR-PL, IRS-SWI

:W/m2/sr/µmIRS-TIR: Kelvin

VNR-NP, VNR-PL, IRS-SWI : SNRIRS-TIR: NE∆T

m

VN1 380 10 60 210 250 250VN2 412 10 75 250 400 250VN3 443 10 64 400 300 250VN4 490 10 53 120 400 250VN5 530 20 41 350 250 250VN6 565 20 33 90 400 250VN7 673.5 20 23 62 400 250VN8 673.5 20 25 210 250 250VN9 763 12 40 350 1200 250/1000VN10 868.5 20 8 30 400 250VN11 868.5 20 30 300 200 250

P1 673.5 20 25 250 250 1000P2 868.5 20 30 300 250 1000

SW1 1050 20 57 248 500 1000SW2 1380 20 8 103 150 1000SW3 1630 200 3 50 57 250SW4 2210 50 1.9 20 211 1000T1 10.8 0.7 300 340 0.2 250/1000T2 12.0 0.7 300 340 0.2 250/1000

Multi-angle obs. for 673.5nm and 868.5nm

250m over the Land or coastal area, and 1km over offshore

-SGLI Specification-

-Bands and lunar phase angle of SGLI, MODIS and VIIRS-

Lunar Phase angle

Period of comparison (Number of Observation)

GCOM-CSGLI-VNR

+7±3 or-7±3 deg

Jan. 31, 2018-Dec. 23, 2018

(20 times)Aqua

MODIS -55.5±1degDec. 30, 2017-Nov. 20, 2018

(12 times)SNPPVIIRS -51±1deg

Dec. 30, 2017-Nov. 20, 2018

(8 times)

• 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 table

Lunar Phase angle and Observation Period

Comparison Bands

2. Methodology

10

• 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, so that the Moon is viewed in the same optical path.

Earth Moon

Maneuver

LunarObservation

-SGLI Lunar Observation Method-

• 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 VNR-NP 11 bands

Lunar digital number response of VN11 obtained by one pitch maneuver

11

NP:400 linePL:100line

NP:160 pixelPL: 30pixel

Integrated Area*

Deep Space

Deep Space

NP:500 linePL:125line

NP:500 linePL:125line

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

Step1The lunar radiance is obtained by the following equation,𝐿𝐿𝑘𝑘,𝑝𝑝 = 𝐺𝐺𝑘𝑘,𝑝𝑝 �

1∆𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠,𝑘𝑘

� 𝐷𝐷𝐷𝐷𝑅𝑅𝑅𝑅𝑅𝑅 − 𝐷𝐷𝐷𝐷𝐷𝐷𝑅𝑅𝑠𝑠𝑘𝑘𝐿𝐿𝑘𝑘,𝑝𝑝:𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟(𝑘𝑘 = 𝑟𝑟𝑐𝑐~11, 𝑝𝑝 = 𝑝𝑝𝑟𝑟𝑝𝑝𝑟𝑟𝑝𝑝)𝐺𝐺𝑘𝑘,𝑝𝑝:𝐺𝐺𝐿𝐿𝑟𝑟𝐿𝐿 𝑝𝑝𝐿𝐿𝑟𝑟𝑝𝑝𝐿𝐿𝐿𝐿𝐿𝐿𝑟𝑟𝑐 𝑚𝑚𝑟𝑟𝐿𝐿𝑚𝑚𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟∆𝐺𝐺𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠,𝑘𝑘:𝐸𝐸𝑝𝑝𝑟𝑟𝑟𝑟𝐸𝐸𝐿𝐿𝑟𝑟𝑟𝑟𝐿𝐿𝑝𝑝 𝑚𝑚𝑐𝐿𝐿𝐸𝐸𝐸𝐸𝑟𝑟𝐿𝐿 𝑟𝑟𝑐𝑐𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟𝐸𝐸𝑟𝑟𝑐𝑐𝐿𝐿 𝑟𝑟𝑐𝑐𝑟𝑟𝑐𝑐𝑐𝑐𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝐿𝐿𝐸𝐸𝐷𝐷𝐷𝐷𝑅𝑅𝑅𝑅𝑅𝑅: 𝐼𝐼𝐿𝐿𝐸𝐸𝑟𝑟𝐼𝐼𝐿𝐿𝐿𝐿𝐸𝐸𝑟𝑟𝑟𝑟 𝑟𝑟𝑟𝑟𝐼𝐼𝑟𝑟𝐸𝐸𝐿𝐿𝑝𝑝 𝐿𝐿𝐿𝐿𝑚𝑚𝑛𝑛𝑟𝑟𝐿𝐿 (4 𝑝𝑝𝑟𝑟𝐿𝐿𝑟𝑟 − 𝑚𝑚𝑟𝑟𝐿𝐿𝐿𝐿 𝐶𝐶𝐶𝐶𝐷𝐷 𝑝𝑝𝑟𝑟𝑝𝑝𝑟𝑟𝑝𝑝𝑚𝑚 × 4 𝑝𝑝𝑟𝑟𝐿𝐿𝑟𝑟)𝐷𝐷𝐷𝐷𝐷𝐷𝑅𝑅𝑠𝑠𝑘𝑘:𝐴𝐴𝐴𝐴𝑟𝑟𝐿𝐿𝐿𝐿𝐼𝐼𝑟𝑟 𝑐𝑐𝑐𝑐 𝑟𝑟𝑟𝑟𝐼𝐼𝑟𝑟𝐸𝐸𝐿𝐿𝑝𝑝 𝐿𝐿𝐿𝐿𝑚𝑚𝑛𝑛𝑟𝑟𝐿𝐿 𝑐𝑐𝑐𝑐 𝑟𝑟𝑟𝑟𝑟𝑟𝑝𝑝 𝑚𝑚𝑝𝑝𝐿𝐿𝑟𝑟𝑟𝑟 𝑐𝑐𝑛𝑛𝑚𝑚 𝑟𝑟𝐿𝐿𝐸𝐸𝐿𝐿 𝐿𝐿𝐸𝐸 𝑟𝑟𝐿𝐿𝑟𝑟𝑐 𝑝𝑝𝑟𝑟𝑝𝑝𝑟𝑟𝑝𝑝

Step2The lunar irradiance is calculated by the following equation,

𝐼𝐼𝑘𝑘 = �𝑝𝑝=1

𝑁𝑁

𝛺𝛺𝑘𝑘,𝑝𝑝𝐿𝐿𝑘𝑘,𝑝𝑝 �1𝑐𝑐𝑜𝑜𝑠𝑠

� sin 𝜃𝜃

𝐼𝐼𝑘𝑘:𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑟𝑟𝐿𝐿𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟𝐿𝐿𝐿𝐿𝑟𝑟𝑟𝑟(𝑘𝑘 = 𝑟𝑟𝑐𝑐~11)𝐷𝐷:𝑇𝑇𝑐𝑐𝐸𝐸𝐿𝐿𝑝𝑝 𝐿𝐿𝐿𝐿𝑚𝑚𝑛𝑛𝑟𝑟𝐿𝐿 𝑐𝑐𝑐𝑐 𝑝𝑝𝑟𝑟𝑝𝑝𝑟𝑟𝑝𝑝𝛺𝛺𝑘𝑘,𝑝𝑝:𝑆𝑆𝑐𝑐𝑝𝑝𝑟𝑟𝑟𝑟 𝐿𝐿𝐿𝐿𝐼𝐼𝑝𝑝𝑟𝑟 𝑝𝑝𝑟𝑟𝐿𝐿 𝑝𝑝𝑟𝑟𝑝𝑝𝑟𝑟𝑝𝑝𝑐𝑐𝑜𝑜𝑠𝑠:𝑂𝑂𝐴𝐴𝑟𝑟𝐿𝐿𝑚𝑚𝐿𝐿𝑚𝑚𝑝𝑝𝑝𝑝𝑟𝑟𝐿𝐿𝐼𝐼 𝑐𝑐𝐿𝐿𝑟𝑟𝐸𝐸𝑐𝑐𝐿𝐿𝜃𝜃:𝐴𝐴𝐿𝐿𝐼𝐼𝑝𝑝𝑟𝑟 𝑛𝑛𝑟𝑟𝐸𝐸𝑏𝑏𝑟𝑟𝑟𝑟𝐿𝐿 𝑚𝑚𝐿𝐿𝐸𝐸𝑟𝑟𝑝𝑝𝑝𝑝𝑟𝑟𝐸𝐸𝑟𝑟 − 𝑚𝑚𝑐𝑐𝑐𝑐𝐿𝐿 𝐴𝐴𝑟𝑟𝑟𝑟𝐸𝐸𝑐𝑐𝐿𝐿 𝐿𝐿𝐿𝐿𝑟𝑟 𝑚𝑚𝐿𝐿𝐸𝐸𝑟𝑟𝑝𝑝𝑝𝑝𝑟𝑟𝐸𝐸𝑟𝑟𝑝𝑝𝑟𝑟𝐸𝐸𝑟𝑟𝑐 𝐿𝐿𝑝𝑝𝑟𝑟𝑚𝑚Step3

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

Step4Evaluate SGLI Measured Irradiance compared to the GIRO Irradiance shown as follows,

𝑅𝑅𝐿𝐿𝐸𝐸𝑟𝑟𝑐𝑐 = �I𝑘𝑘𝑀𝑀𝑠𝑠𝑅𝑅𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑀𝑀 I𝑘𝑘𝐺𝐺𝐺𝐺𝑅𝑅𝐺𝐺 𝑅𝑅𝑠𝑠𝑅𝑅

3. Results

13

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

Normalized by 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 well known, 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.• No degradations of the telescope at long wavelengths are observed.

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

Band Ave. Std Band Ave. Std Band Ave. StdVN1 1.093 ±0.008 - - - - - -VN2 1.091 ±0.008 B8 1.117 ±0.007 M1 1.151 ±0.003VN3 1.068 ±0.008 B9 1.095 ±0.005 M2 1.085 ±0.002

- - - B3 1.089 ±0.006 - - -VN4 1.084 ±0.008 B10 1.092 ±0.005 M3 1.121 ±0.003VN5 1.092 ±0.006 B11 1.062 ±0.005 - - -

B12 1.077 ±0.006B4 1.057 ±0.006

- - - B1 1.057 ±0.007 - - -VN7 1.058 ±0.004 B13 1.064 ±0.006VN8 1.065 ±0.003 B14 1.071 ±0.006VN9 1.073 ±0.004 - - - M6 1.110 ±0.005VN10 1.028 ±0.004VN11 1.040 ±0.004

- - - B17 1.143 ±0.005 - - -

M7 1.1141.101 ±0.006B2 ±0.004

SGLI/GIRO MODIS/GIRO VIIRS/GIRO

VN6 1.068 ±0.006 M4 1.098 ±0.005

M5 1.101 ±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)-

SGLI/MODIS MODIS/VIIRS VIIRS/SGLIBias(min. Band) 0.6% 0.9% 1.6%Bias(max. Band) 6.6% 3.7% 7.7%Uncertainty 3.8% 2.7% 3.4%

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

�𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝑀𝑀𝑀𝑀𝑠𝑠 2)𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀(𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺)

• The sources of uncertainty in these comparisons are Standard deviation of one-year

observations(<1%) Associated with prelaunch characterization of

SGLI (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%)

• The relative biases and uncertainty between the instruments are derived and reported in the table.

• There are slightly larger biases between SGLI and other instruments

4. Discussion

Fits to Lunar Calibration Time Series Residuals Libration vs Phase angleSGLI

(VN1-6)

SGLI(VN7-11)

• A time series of measured responses of VN1-VN6 normalized to the GIRO model are shown in the figure on the upper left,and the lunar time series are fit by exponential functions of time.

• In the same manner, a timeseries of measured response of VN7-VN11 normalized to the GIRO model are shown in the figure on the lower left, and the lunar time series are fit by constant value of time. 17

-Phase Angle Dependency (1/2)-• The residuals of the fits are shown (Center)

Weak correlation between Residuals and Libration(SGLI/GIRO)

Strong correlation between Residuals and Phase angle (SGLI/GIRO)

• The libration angles for the selenographic longitude and latitude of the spacecraft and the Sun are shown (Upper right)

• The phase angle time series at each lunar calibration is shown (Lower right)

-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's lunar empirical model of irradiance has been developed that treats phase and libration.

• The magnitude of the phase angle effects are ten to twenty times greater than other effects including libration.

ROLO model

Hugh H. Kieffer and Thomas C. Stone, “The spectral irradiance of the moon,” The Astronomical Journal, 129:2887-2901, 2005

S. Lachérade, O. Aznay, B. Fougnie, L. Lebègue, “POLO: a unique dataset to derive the phase angle dependence of the Moon irradiance,” Proc. SPIE 9241, Sensors, Systems, and Next-Generation Satellites XVIII, 924112 (7 October 2014); doi: 10.1117/12.2067283

ROLO model vs PLEIADES observation

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

-Comparison of SGLI/SeaWiFS and MODIS/VIIRS over Wavelength-

• In addition, we found that SeaWiFS, which observed the moon at phase angle of 7 deg., has similar 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 in the 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 and PLEIADES.

• 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.

+ SeaWiFS (Phase angle = ＋7 deg.)

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

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 from

the near-UV (380nm) to the near-infrared wavelength(868nm).• Time Series of Measured(SGLI)/Model(GIRO) are analyzed and degradations of the

telescope at short wavelengths (from 380nm to 565nm) are clearly observed as expected.

• The residual of phase angle dependence of the ROLO model has been observed in SGLI 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. 2018

Vegetation distribution of Japan Coral reefs in the Bahamas Namibia coast and desert Morning glow of Kamchatka peninsula

https://gportal.jaxa.jp/

SGLI scientific products had been released to public on Dec. 2018 via JAXA’s data distribution system, G-Portal.

• 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.)