Status of S-NPP VIIRS Solar and Lunar Calibration X. Xiong 1, N. Lei 2, J. Fulbright 2, and Z. Wang 2 1 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 2 Science 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) 1
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 2
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 3
Background 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 VIIRS On-board Calibrators (MODIS heritage) Solar diffuser Solar diffuser stability monitor Blackbody S-NPP 4
16 Moderate (radiometric) bands, 5 Imaging bands, 1 DNB VIIRS VIIRS Spectral Bands MODIS Substitute 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 10 0.459-0.479 500 0.483-0.493 1000 M4 0.545-0.565 750 4 or 12 0.545-0.565 500 0.546-0.556 1000 I1 0.600-0.680 375 1 0.620-0.670 250 M5 0.662-0.682 750 13 or 14 0.662-0.672 1000 0.673-0.683 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 16 or 2 0.862-0.877 0.841-0.876 1000 250 M7 0.846-0.885 750 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 I5 10.500-12.400 375 31 or 32 31 10.780-11.280 1000 10.780-11.280 11.770-12.270 1000 1000 M16 11.538-12.488 750 32 11.770-12.270 1000 1 DNB: L/M/HG 32 Agg. Modes 14 RSB: 0.41-2.3 mm 7 DGB: M1-M5, M7, and M13 7 TEB: 3.7-12.1 mm 5
VIIRS Solar and Lunar Calibration: Approaches Solar Diffuser Stability Monitor Solar Diffuser Solar Calibration: each orbit SDSM Operation: Currently 3/week (more frequent at mission beginning) Rotating Telescope Aft Optics and HAM Extended SV Port 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 6
VIIRS Solar and Lunar Calibration: Methodologies Radiance (L) Retrieval: F SD L F L L L SUN SD, PL PL F c0 c1 dn c2 dn F: Calibration scaling factor derived from on-orbit calibration c i : Calibration coefficients determined from pre-launch calibration RVS: Response versus scan angle Solar Calibration: L SUN : Expected solar radiance reflected from SD panel L SD,PL : Measured solar radiance using PL calibration coefficients L SUN E SUN 2 RVS BRDF( t) cos SDS inc Lunar Calibration: F MOON I I ROLO ROLO MOON, PL LMOON, PL B det, sam, scan I g / N SCAN I SUN : Lunar irradiance (integrated) from ROLO model I SD,PL : Lunar irradiance determined using PL calibration coefficients N SCAN, B, g: number of scans, pixel solid angle, aggregation factor 7
On-orbit Improvements and Performance SD Screen Transmission ( SD ) and BRDF SD 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 8
On-orbit Pre-launch SD Screen Transmission ( SD ) and BRDF SD 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 LUT Ratio On-orbit LUT: Larger range Better resolution Same wavelength 9
SDSM Screen Transmission ( SDSM ) SDSM PL_LUT SDSM Yaw_LUT SDSM New_LUT Improvements of SDSM Screen SDSM LUT => smooth SD degradation (H-factor) trend 10
Comparison of H- and F-factors derived from different LUTs PL LUT and New LUT YAW LUT and New LUT H: F: 11
Solar Vector Error (in SDR Common Geo Library) 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. ΔF VISNIR ΔH ΔF SWIR The cos θ SD factor is used in the H- and F-factor calculations. 12
Comparison of Solar and Lunar Calibration Lines - SD Cal Symbols - Lunar Cal 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 13
Number of Scans Used in Lunar Calibration Center 2 scans Center 4 scans Average and standard deviation of all individual scans 14
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) 15
On-orbit Modulated RSR 16
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) 17
Modulated RSR Impact on SD and Lunar Calibration Large changes at mission beginning Caution: use and comparison of solar and lunar F-factors for M1 and DNB 18
On-orbit Improvements and Performance SD Screen Transmission ( SD ) and BRDF SD SDSM Screen Transmission ( SDSM ) Correction for Solar Vector Error in SDR Comparison of Solar and Lunar Calibration Modulated RSR Poster by Sherry Chen et al on VIIRS DNB calibration performance assessment. 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 19
Impact due to SDSM OOB Responses (Illustration) SD degradation presentation (Xiong et al, CALCON 2016 Monday) M1 RSR used as D1 RSR (illustration) Changes in SDSM detector responses OOB response impact and its on-orbit change Accurate SD degradation characterization is critical to high quality RSB calibration 20
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) Pleiades: POLO Impact due to phase angles 21
Future Work 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) 22