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Status of S-NPP VIIRS Solar and Lunar Calibration

X. Xiong1, N. Lei2, J. Fulbright2, and Z. Wang2

1NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA2Science Systems and Applications Inc., Lanham, MD 20760, USA

(J. Fulbright: currently with Columbus Technologies and Services, Inc.)

CALCON 2015, Logan, UT, August 24-27, 2015)

• Acknowledgements– VIIRS Characterization Support Team (VCST)

– MODIS Characterization Support Team (MCST)

– S-NPP Mission Operation Team (MOT)

– USGS T. Stone

• Collaborative Effort– NOAA JPSS VIIRS SDR Team

– Aerospace Corporation

– Others…

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Outline

• Background

• VIIRS Solar and Lunar Calibration– Calibration Approaches and Methodologies

• On-orbit Improvements and Performance– Improvements

– Comparison of Solar and Lunar Calibration

– Challenging Issues

• Future Work

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Visible Infrared Imaging Radiometer Suite (VIIRS)• VIIRS on Suomi National Polar-orbiting Partnership (S-NPP) Satellite

‒ Successfully operated for more than 3.5 years since Oct. 2011

• VIIRS on Future JPSS Missions

‒ J1 launch in late 2016 (early 2017)

‒ J2 launch in 2020

• 22 Spectral Bands

‒ 14 reflective solar bands (RSB) & a DNB: 0.4-2.3 mm

‒ 7 thermal emissive bands (TEB): 3.7-12.1 mm

‒ Moderate/Imaging bands: 750/375 m nadir spatial resolution

‒ Dual gain bands: M1-M5, M7, and M13

• On-board Calibrators (MODIS heritage)

‒ Solar diffuser

‒ Solar diffuser stability monitor

‒ Blackbody

S-NPP

VIIRS

Background

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VIIRS Spectral Bands

VIIRS Band Spectral Range (um) Nadir HSR (m) MODIS Band(s) Range HSR

DNB 0.500 - 0.900

M1 0.402 - 0.422 750 8 0.405 - 0.420 1000

M2 0.436 - 0.454 750 9 0.438 - 0.448 1000

M3 0.478 - 0.498 750 3 100.459 - 0.479

0.483 - 0.493

500

1000

M4 0.545 - 0.565 750 4 or 120.545 - 0.565

0.546 - 0.556

500

1000

I1 0.600 - 0.680 375 1 0.620 - 0.670 250

M5 0.662 - 0.682 750 13 or 140.662 - 0.672

0.673 - 0.683

1000

1000

M6 0.739 - 0.754 750 15 0.743 - 0.753 1000

I2 0.846 - 0.885 375 2 0.841 - 0.876 250

M7 0.846 - 0.885 75016 or 2

0.862 - 0.877

0.841 - 0.876

1000

250

M8 1.230 - 1.250 750 5 SAME 500

M9 1.371 - 1.386 750 26 1.360 - 1.390 1000

I3 1.580 - 1.640 375 6 1.628 - 1.652 500

M10 1.580 - 1.640 750 6 1.628 - 1.652 500

M11 2.225 - 2.275 750 7 2.105 - 2.155 500

I4 3.550 - 3.930 375 20 3.660 - 3.840 1000

M12 3.660 - 3.840 750 20 SAME 1000

M13 3.973 - 4.128 750 21 or 22 3.929 - 3.989

3.929 - 3.989

1000

1000

M14 8.400 - 8.700 750 29 SAME 1000

M15 10.263 - 11.263 750 31 10.780 - 11.280 1000

I5 10.500 - 12.400 375 31 or 3210.780 - 11.280

11.770 - 12.270

1000

1000

M16 11.538 - 12.488 750 32 11.770 - 12.270 1000

VIIRS MODIS Substitute

1 DNB: L/M/HG32 Agg. Modes

14 RSB:0.41-2.3 mm

7 TEB:3.7-12.1 mm

7 DGB:

M1-M5, M7, and M13

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Mo

de

rate

(ra

dio

met

ric)

ban

ds,

5 Im

agin

g b

and

s, 1

DN

B

Rotating Telescope Aft Optics and HAM

Solar Diffuser

Solar DiffuserStability Monitor

Extended SV Port

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• Lunar Calibration: 8-9 times/year (33 since launch)

– Planned at the “same” lunar phase angles (-51⁰)

– Implemented via S/C roll maneuvers

– Viewed through space view (SV) port

Solar Calibration: each orbit

SDSM Operation:Currently 3/week (more frequent at mission beginning)

VIIRS Solar and Lunar Calibration: Approaches

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RVSdncdnccFLFL PL2

210 Radiance (L) Retrieval:

PLSD

SUNSD

L

LF

,

SCAN

scansam

PLMOON

ROLO

PLMOON

ROLOMOON

NL

I

I

IF

/g,det,

B,,

Solar Calibration:

Lunar Calibration:

F: Calibration scaling factor derived from on-orbit calibration

ci: Calibration coefficients determined from pre-launch calibration

RVS: Response versus scan angle

LSUN: Expected solar radiance reflected from SD panelLSD,PL: Measured solar radiance using PL calibration coefficients

ISUN: Lunar irradiance (integrated) from ROLO modelISD,PL: Lunar irradiance determined using PL calibration coefficientsNSCAN, B, g: number of scans, pixel solid angle, aggregation factor

VIIRS Solar and Lunar Calibration: Methodologies

incSDSSUNSUN tBRDFEL cos)(

On-orbit Improvements and Performance

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SD Screen Transmission (SD) and BRDFSD

SDSM Screen Transmission (SDSM)

Correction for Solar Vector Error in SDR

Comparison of Solar and Lunar Calibration

Modulated RSR

more than two versions

by different groups

with independent effort

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SD LUT Ratio

On-orbit LUT:

Larger rangeBetter resolutionSame wavelength

Pre

-lau

nch

On

-orb

it

Initial SD and SDSM LUTs derived from “limited” pre-launch measurements

On-orbit improvements made using data collected during SC yaw maneuvers

Latest improvements achieved by adding regular on-orbit calibration data to fill the gaps in yaws

SD Screen Transmission (SD) and BRDFSD

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SDSM PL_LUT SDSM New_LUTSDSM Yaw_LUT

Improvements of SDSM Screen SDSM LUT => smooth SD degradation (H-factor) trend

SDSM Screen Transmission (SDSM)

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Comparison of H- and F-factors derived from different LUTs

PL LUT and New LUT YAW LUT and New LUT

H:

F:

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• A mismatch of ECI (Earth-Centered Inertial) frames when computing the

transformation to spacecraft frame library leads to a slight, but important

(~0.2 deg.) error in the solar angles used in the RSB radiometric

calibration.

Solar Vector Error (in SDR Common Geo Library)

ΔH

ΔF VISNIR

ΔF SWIR

• The cos θSD factor is used in the

H- and F-factor calculations.

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Comparison of Solar and Lunar Calibration

SD and lunar calibration made at the “same” angle of incidence (AOI)

Large changes in NIR/SWIR response due to telescope mirror degradation

Modulated RSR and fitted SD degradation applied

Use of measured SD degradation reduces some seasonal variations in 1/F-factors

Lines - SD Cal

Symbols - Lunar Cal

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Number of Scans Used in Lunar Calibration

Center 2 scans

Center 4 scans

Average and standard deviation of all individual scans

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Detector-dependent vs Band-averaged

Also examined are the mirror side differences and lunar irradiance retrieved using all detectors and all scans (over-sampling factor used)

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On-orbit Modulated RSR

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On-orbit Modulated RSR

l dependent optics degradation

DNB

Small impact on bands with narrow bandwidths and small OOB responses; large impact on DNB (broad bandwidth)

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Modulated RSR Impact on SD and Lunar Calibration

Caution: use and comparison of solar and lunar F-factors for M1 and DNB

Large changes atmission beginning

On-orbit Improvements and Performance

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SD Screen Transmission (SD) and BRDFSD

SDSM Screen Transmission (SDSM)

Correction for Solar Vector Error in SDR

Comparison of Solar and Lunar Calibration

Modulated RSR

• Challenging Issues

₋ Solar calibration

Impact due OOB responses in SDSM and VIIRS spectral bands because of wavelength-dependent degradation

Direct impact of SD degradation on RSR calibration

₋ Lunar calibration

Improved lunar phase/libration correction needed

Poster by Sherry Chen et al on VIIRS DNB calibration performance assessment.

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Impact due to SDSM OOB Responses (Illustration)

M1 RSR used as D1 RSR (illustration) Changes in SDSM detector responses

Accurate SD degradation characterization is critical to high quality RSB calibration

OOB response impact and its on-orbit change

SD degradation presentation (Xiong et al, CALCON 2016 Monday)

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Lunar Phase and Libration Correction

Similar feature for M1-M4 and I1 Improvements for SWIR SD calibration

Phase angle dependence of the ROLO model (blue bands)

Impact due to phase anglesPleiades: POLO

Future Work

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• VIIRS solar and lunar calibration activities have been successfully planned and executed regularly in support of its RSB on-orbit calibration

– Mission consistent calibration LUTs (mainly for RSB) have been generated in support of SDR and EDR data product quality assessment (and data production)

• Continuing effort on calibration improvements and data quality assurance

– VIIRS unique feature: modulated RSR (time-dependent)

– OOB responses of SDSM detectors (time-dependent)

– Lunar calibration uncertainty contributors (short- and long-term)

– Improved ROLO reference (from USGS/T. Stone)

– Lessons from Terra/Aqua MODIS, SeaWIFS, and other solar and lunar calibration (similarity and difference)