NPP VIIRS Pre-Launch Performance and SDR Validation

1. NPP VIIRS Pre-Launch Performance and SDR Validation Frank De Luccia, The Aerospace Corporation, El Segundo, CA Bruce Guenther, NOAA - Joint Polar Satellite System, Goddard Space Flight Center, Greenbelt, MD Chris Moeller, University of Wisconsin, Madison, WI, XiaoxiongXiongand Robert Wolfe , NASA’s Goddard Space Flight Center, Greenbelt, MD 2011 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) 24-29 July, Vancouver, Canada

2. Topics • Instrument Background • Pre-Launch Performance • Comparisons to MODIS Aqua as reference • Spectral characteristics • Spatial characteristics • Radiometric sensitivity - SNR and NEdT • Polarization sensitivity • Performance summary and issues • SDR Validation • Calibration and Validation (Cal/Val) team • Cal/Val plans and task structure • Principal activities per Cal/Val phase • Summary

3. Instrument Background

4. Instrument Background • NPP VIIRS manufactured by Raytheon under subcontract to Northrop Grumman for NPOESS • NPP instruments now under JPSS program management • VIIRS design draws on MODIS heritage • MODIS also built by Raytheon (SBRS) • On-board calibrators and calibration strategy very similar

5. Instrument Background – cont’d

6. Environmental Data Products (EDRs) Derived from VIIRS Sensor Data Records (SDRs) * * Key Performance Parameter (KPP) ** Intermediate Product (not an EDR)

7. Pre-Launch Performance

8. VIIRS Spectral Characteristics • VIIRS has 22 bands from 0.4 m to 12.5 m (8 dual gain) • 7 moderate resolution, 2 imaging resolution and 1 broadband day/night band in 0.4 to 1.0 m range • 6 moderate resolution and 2 imaging resolution bands in 1 to 5 m range • 3 moderate resolution and 1 imaging resolution bands in 5 to 15 m range

9. VIIRS Spatial Characteristics • 16 moderate resolution bands with 750 m footprint at nadir • 5 imaging resolution bands with 375 m footprint at nadir • 1 DNB with 750 m footprint constant across scan. • Pixel aggregation used to control footprint growth across scan.

10. VIIRS Radiometric Sensitivity • VIIRS SNR and NEdT are comparable or superior to MODIS SNR and NEdT when normalized to the same spatial scale and the same radiance level

11. VIIRS Polarization Sensitivity • VIIRS polarization performance is generally better than that of MODIS. • Unlike MODIS, NPP VIIRS polarization sensitivity varies strongly with field angle resulting in detector dependence. • VIIRS pre-launch characterization provides high-quality, per-pixel characterization of polarization sensitivity and phase for use in data product processing.

12. Performance Summary and Issues • VIIRS performance is comparable or superior to that of MODIS Aqua in corresponding bands in all key performance areas except crosstalk and out-of-band spectral response. • NPP VIIRS has optical crosstalk in the VisNIR (0.8% average) due to high angle scattering in the spectral filters • May impact Ocean Color/Chlorophyll and Aerosol data products. • NPP VIIRS out-of-band (OOB) spectral response somewhat higher than MODIS Aqua due to same scattering mechanism in filters • Second and subsequent VIIRS flight units will have reduced optical crosstalk and OOB response due to improved spectral filters. • VIIRS polarization sensitivity is lower than that of MODIS Aqua but is detector dependent • Requires per-pixel correction in Ocean Color processing • Banding effects in SDRs displayed as images • In other key performance areas not addressed here, such as band-to-band registration, near-field response and stray light response, VIIRS performance compares favorably with that of MODIS Aqua.

13. SDR Validation

14. VIIRS SDR Cal/Val Team

15. Evolution of VIIRS Calibration and Validation Plans • On-orbit cal/val tasks were defined in an intensive government-contractor team collaboration • Cal/val strategies draw heavily on MODIS experience • Inputs on specific activities distilled into 54 tasks • VIIRS SDR Calibration Plan produced and peer reviewed in 2009 • Comprehensive description of VIIRS calibration program • Describes team, team interactions, tasks, tools and ground truth resources • Maps cal/val activities into cal/val phases • Provides metrics for evaluating SDR product maturity • VIIRS SDR Calibration/Validation Operations Concept (OPSCON) Document developed in 2011 • Infrastructure support definition • Data flow and process definition to support cal/val rehearsals • Managerial leadership has transitioned to Changyong Cao of NOAA STAR • Roles and responsibilities have evolved to reflect increased participation of NOAA STAR

16. Six Broad Categories of On-Orbit Cal/Val Tasks • Functional Performance and Format Evaluation (FPF 1-7) • FPF tasks involve evaluating instrument functions and verifying the correctness of data formats. Performed early in the mission, and will not be repeated unless the instrument suffers a catastrophic event. • Calibration System Evaluation (CSE 1-6) • CSE tasks evaluate the performance of the onboard calibration system and update the calibration algorithm databases accordingly. • Image Quality Evaluation (IMG 1-4) • IMG tasks evaluate the quantitative and qualitative spatial performance characteristics of the instrument. • Radiometric Evaluation (RAD 1-25) • RAD tasks evaluate the radiometric performance of the data product algorithm. Radiometric evaluation will include evaluation of spectral characteristics since changes in these characteristics relative to the pre-launch baseline will mainly manifest themselves as in-band radiometric errors. • Geolocation Evaluation (GEO 1-7) • GEO tasks evaluate the geolocation accuracy of the data product. • Performance and Telemetry Trending (PTT 1-5) • PTT tasks evaluate long-term changes in the performance of both the instrument and the data product.

17. Pre-Launch Activities • Continued analysis and refinement of performance baseline based on test program • Verification of at-launch SDR algorithm look-up tables (LUTs) • Improvements where warranted • Operational code review and error checking • Cal/val tool development • RDR and SDR readers, LUT readers/writers • Custom tools for cal/val analysis tasks • Practice and training in operation of VIIRS SDR operational code • Algorithm Development Library (ADL) version of code allows cal/val team to modify and test LUT updates and potential algorithm improvements • Task rehearsals to demonstrate readiness for on-orbit cal/val

18. Early Orbit Checkout (EOC) • Verify instrument operability and functionality • Signal • Noise • Scan rate • Compare signal and noise characteristics to pre-launch baseline • Verify RDR, SDR and intermediate product formats and validity of content • Early use of Solar Diffuser Stability Monitor • Critical for beginning time series to trend change in Solar Diffuser reflectance

19. Intensive Calibration & Validation (ICV) • Radiance match-ups • Ground sites • Inter-satellite comparisons • Comparisons with Cross-Track Infrared Sounder (CrIS) • Aircraft underflights • Geolocation match-ups • Ground Control Points (GCPs) from Landsat • Feedback on SDR quality from EDR validation efforts • Maneuvers • Exploitation of lunar data • SDR algorithm tuning and LUT updates • Continued performance and telemetry trending Objective is achievement of stable, “validated/calibrated” SDRs by end of ICV.

20. Long-Term Monitoring (LTM) • Routine performance of reflective band off-line calibration • Periodic measurement and trending of key instrument characteristics • Operability • Noise/SNR • Gains • Critical temperatures, voltages, currents in telemetry • Periodic repetition of ICV tasks to maintain calibration and SDR quality • Radiometry • Geolocation

21. VIIRS Cal/Val Activitiesby Phase

22. SDR Product Maturity Levels • Beta • Early release product, initial calibration applied, minimally validated and may still contain significant errors • Available to allow users to gain familiarity with data formats and parameters • Product is not appropriate as the basis for quantitative scientific publications studies and applications • Provisional • Product quality may not be optimal • Incremental product improvements are still occurring as calibration parameters are adjusted with sensor on-orbit characterization • General research community is encouraged to participate in the QA and validation of the product, but need to be aware that product validation and QA are ongoing • Users are urged to contact NPP Cal/Val Team representatives prior to use of the data in publications • Validated/Calibrated • On-orbit sensor performance characterized and calibration parameters adjusted accordingly • Ready for use by the Centrals, and in scientific publications • There may be later improved versions

23. Inter-Satellite Comparisons • Analysis of Simultaneous Nadir Overpass (SNO) data from VIIRS and other satellites will reveal relative biases • Off-nadir inter-satellite comparisons will be exploited also, particularly to evaluate Response vs Scan Angle effects • Leverages validation performed for other satellite systems • VIIRS/MODIS comparisons expected to be particularly useful • MODIS instruments well validated • Many similar bands with similar radiometric performance MODIS Terra/AVHRR 11 m Band Comparison (Xiong et al., CEOS-IVOS 2004)

24. CrIS-VIIRS Cal/Val (heritage AIRS-MODIS) Abundant matchups on every Aqua orbit. 14 orbits per day (>10E6 matchups/day) Radiometric performance as function of scene temperature AIRS footprints overlain on MODIS image. Filter the sample to retain spatially uniform scenes. Radiometric performance as function of scan mirror angle

25. Use of Maneuvers for VIIRS SDR Validation (1) • S/C Maneuvers for VIIRS Calibration • Scientific benefits and implementation strategies are based on lessons and experience from heritage missions and sensors, such as MODIS and SeaWiFS • All 3 types of VIIRS maneuvers have been approved for the NPP mission • Roll Maneuvers • Near monthly event with lunar phase angles at 55 degree and roll angles less than -14 degrees • Provide an accurate and long-term monitoring of VIIRS RSB calibration stability and independent monitoring of SD degradation • Yaw Maneuvers • Once during initial S/C checkout; could repeat every 3 years depending on the SD degradation rate • Validate SD solar attenuation screen (SAS) and SDSM sun view screen transmission as a function of solar illumination angles and assure VIIRS SDR quality for the RSB

26. Use of Maneuvers for VIIRS SDR Validation (2) • Pitch Maneuvers • Once during initial S/C checkout; could repeat depending on scan-angle dependent changes in TEB responses • Validate sensor response versus scan angle (RVS) and assure VIIRS SDR quality for the TEB • Operation and Data Analysis Support • Maneuver implementation working group established to coordinate among different groups (and instruments) • VIIRS maneuver data analysis tools developed primarily from MODIS experience

27. Use of Lunar Data for VIIRS SDR Validation (1) • Track Changes in Sensor Responses for VIIRS Reflective Solar Bands • Both MODIS and SeaWiFS have used lunar time series to track changes in sensor responses; lunar viewing geometry corrections are made using ROLO lunar model • Provide Independent Monitoring of VIIRS Solar Diffuser Degradation • The angle of incidence (AOI) of VIIRS space view, through which the lunar observations are made, is identical to the AOI of SD observations • Enable Calibration Inter-comparison with Other Sensors (e.g. MODIS) • This is similar to the effort made to inter-compare Terra and Aqua MODIS, MODIS and SeaWiFS

28. Use of Lunar Data for VIIRS SDR Validation (2) SeaWiFS Normalized Lunar Radiance Terra and Aqua MODIS B1 Lunar Irradiance

29. VIIRS Geolocation Matchups • Number of Control Point Matchups • Example of first 90 days of control point matchups from MODIS/Terra • Good (> 60% normalized cross correlation) control point matchups per day: 260 • Used to perform initial refinement of instrument to spacecraft alignment and to refine rotating telescope and half angle mirror geometric parameters • Track Residuals (nadir adjusted) • Scan Residuals (nadir adjusted)

30. Aircraft Campaigns • Aircraft underflights can provide high quality radiometric validation across the VIIRS spectrum • Direct observations of the integrated upwelling earth scene radiance in nearly same time, space, and geometry as the on-orbit sensor • NIST traceable uncertainties for some airborne instruments • Approach based upon heritage validation of AIRS, MODIS, IASI. • Preliminary plans for aircraft campaigns have been developed but are currently “on hold” due to funding constraints • Platforms: ER-2 and/or WB-57 • Instruments desired for VIIRS SDR validation • Enhanced MODIS Airborne Simulator (EMAS) • 50 channel Vis/IR spectrometer, 50 m resolution, 36 km swath • Expected to include reflective solar band (RSB) Hyperspectral Imager (HSI) • Scanning High-resolution Interferometer Sounder (SHIS) • Scanning M/LWIR 0.5 cm-1 interferometer, 2 km resolution, 32 km swath • NIST traceable calibration • NPOESS Airborne Sounder Testbed (NAST-I) • Scanning MWIR/LWIR interferometer, 2km resolution, 40 km swath • NIST traceable calibration • Cloud Physics Lidar (CPL) • Micropulse dual polarization lidar, 15 m resolution, nadir only

31. 11.01 um MODIS on Terra/Aqua SHIS, etc. on ER-2 705 km 20 km q Histogram of radiometric matchups Approach based upon heritage efforts for AIRS and MODIS Fly instrumented ER-2 along satellite track Matching geometry of earth scene observations

32. Summary • VIIRS calibration and validation plans draw heavily on MODIS strategies and experience • Similar data products • Similar on-board calibrators • Similar radiometric and geolocation retrieval approaches • VIIRS pre-launch performance baseline very well established • Extensive instrument characterization provided in test program • Independent data analysis by multiple contractor and government teams has provided highly reliable parameter values for SDR algorithm LUTs • Experienced, multi-organization calibration/validation team is well prepared to execute VIIRS on-orbit validation