NPP VIIRS Pre-Launch Performance and SDR Validation

Frank De Luccia, The Aerospace Corporation, El Segundo, CABruce Guenther, NOAA - Joint Polar Satellite System, Goddard Space Flight

Center, Greenbelt, MDChris Moeller, University of Wisconsin, Madison, WI,

Xiaoxiong Xiong and 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

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

VIIRS MODISOrbit 824 km, sun-synchronous,

near-polar705 km, sun-synchronous,near-polar

Scan Rate 33.6 rpm, cross-track 20.3 rpm, cross-track

Swath Dimensions

3000 km across track by 13 km along track at nadir

2330 km across track by 10 km along track at nadir

Size 1.3 m x 1.4 m x 0.9 m 1.0 m x 1.6 m x 1.0 m

Weight 263 kg 250 kg

Power 154 W 225 W

Data Rate 10.4 Mbps (peak) 11 Mbps (peak)

Quantization 12 bits 12 bits

Design Life 7 years 5 years

5

Instrument Background – cont’d

Flat-panel Cryoradiator

4-Mirror Anastigmat(FMA) All Reflective

Aft Optics Imager

3-Mirror Anastigmat(TMA) All reflectiveRotating telescope

MODISBlackbody

MODISSolar Diffuser

Half-angle Mirror

Separately Mounted Electronics Module

Cold FPADewar Assembly

MODIS derivedSolar DiffuserStability Monitor(SDSM)

6

Environmental Data Products (EDRs) Derived from VIIRS Sensor Data Records (SDRs)

Product Group EDRs/Other ProductsImagery Imagery*

Surface Temperatures

Sea Surface Temperature Land Surface TemperatureIce Surface Temperature

Clouds Cloud Base Height Cloud Top HeightCloud Cover/Layers Cloud Top PressureCloud Particle Size Cloud Top TemperatureCloud Optical Thickness Cloud Mask**

Aerosols Aerosol Optical Thickness Aerosol Particle Size

Ocean Biosphere Ocean Color/Chlorophyll

Land Biosphere Vegetation Index AlbedoVegetation Type

Snow & Sea Ice Snow Cover Sea Ice Characterization

Fire Fire Detection

Other Soil Moisture Suspended MatterNet Heat Flux Geolocation**

* Key Performance Parameter (KPP)** Intermediate Product (not an EDR)

*

Pre-Launch Performance

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VIIRS Spectral Characteristics

MODIS - 1000 m

MODIS - 500 m

MODIS - 250 m

VIIRS - 750 m

VIIRS - 375 m

Wavelength (microns)

AtmosphericTransmission

(Mid-latitudeSummer)

H2O N2O CO2, N2OH2O H2O, CO2H2OH2O

H2O

VIIRS and MODIS Spectral Coverage: 1 m to 5 m

MODIS - 1000 m

MODIS - 500 m

MODIS - 250 m

VIIRS - 750 m

VIIRS - 375 m

Wavelength (microns)

AtmosphericTransmission

(Mid-latitudeSummer)

H2O

H2OH2O

O2

H2O

O2

VIIRS and MODIS Spectral Coverage: 0.4 m to 1.0 m VIIRS and MODIS Spectral Coverage: 5 m to 15 m

Wavelength (microns)

MODIS - 1000 m

MODIS - 500 m

MODIS - 250 m

VIIRS - 750 m

VIIRS - 375 m

CO2O3H2O H2O

• 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

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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.

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60

Alon

g-Sc

an G

roun

d Sa

mpl

ing

Inte

rval

(km

)

Scan Angle (deg)

VIIRS 375 M

VIIRS 750 M

MODIS 250 M

MODIS 500 M

MODIS 1000 M

VIIRS and MODIS Along-Scan Spatial Sampling

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60

Alon

g-Tr

ack

Gro

und

Sam

plin

g In

terv

al (k

m)

Scan Angle (deg)

VIIRS 375 M

VIIRS 750 M

MODIS 250 M

MODIS 500 M

MODIS 1000 M

VIIRS and MODIS Along-Track Spatial Sampling

SA = Scan AngleAgg = Aggregation

1104 m

630 m

1260 m

Agg = 2 : 132 deg < |SA| < 45 deg

1600 m

1600 m

Agg = 1 : 145 deg < |SA| < 56 deg

742 m

262 m

786 m

Agg = 3 : 1|SA| < 32 deg

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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

Comparison of VIIRS and MODIS Aqua Reflected Solar Band SNR

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

M1/8 M2/9 M3/3 M3/10 M4/4 M4/12 I1/1 M5/13 M5/14 M6/15 I2/2 M7/2 M7/16 M8/5 M9/26 I3/6 M10/6 M11/7

SNR

MODIS Aqua PL MODIS Aqua On-Orbit VIIRS PL VIIRS PL Scaled

bette

r

0.001

0.01

0.1

1

I4/20 M12/20 M13/21 M13/22 M14/29 M15/31 I5/31 I5/32 M16/32

NEdT (K)

MODIS Aqua PL MODIS Aqua On-Orbit VIIRS PL VIIRS PL Scaled

Comparison of VIIRS and MODIS Aqua Thermal Emissive Band NEdT

bette

r

VIIRS Band Spectral Range (um) Nadir HSR (m) MODIS Band(s) Range HSRDNB 0.500 - 0.900

M1 0.402 - 0.422 750 8 0.405 - 0.420 1000M2 0.436 - 0.454 750 9 0.438 - 0.448 1000

M3 0.478 - 0.498 750 3 10 0.459 - 0.479 0.483 - 0.493

500 1000

M4 0.545 - 0.565 750 4 or 12 0.545 - 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 14 0.662 - 0.672 0.673 - 0.683

1000 1000

M6 0.739 - 0.754 750 15 0.743 - 0.753 1000I2 0.846 - 0.885 375 2 0.841 - 0.876 250

M7 0.846 - 0.885 750 16 or 2 0.862 - 0.877 0.841 - 0.876

1000 250

M8 1.230 - 1.250 750 5 SAME 500M9 1.371 - 1.386 750 26 1.360 - 1.390 1000I3 1.580 - 1.640 375 6 1.628 - 1.652 500

M10 1.580 - 1.640 750 6 1.628 - 1.652 500M11 2.225 - 2.275 750 7 2.105 - 2.155 500

I4 3.550 - 3.930 375 20 3.660 - 3.840 1000M12 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 32 10.780 - 11.280 11.770 - 12.270

1000 1000

M16 11.538 - 12.488 750 32 11.770 - 12.270 1000

VIIRS MODIS Substitute

Dual-gain Band

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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.

VIIRS VisNIR Polarization Sensitivity

0%

1%

2%

3%

4%

5%

6%

300 400 500 600 700 800 900

Max

. Pol

ariz

atio

n Se

nsiti

vity

(%)

Band Center Wavelength (nm)

-55.5 deg-45 deg-22 deg-8 deg+20 deg+45 deg+55.5 deg

0%

1%

2%

3%

4%

5%

6%

300 400 500 600 700 800 900 1000

Max

. Pol

ariz

atio

n Se

nsiti

vity

(%)

Band Center Wavelength (nm)

-45 deg-22.5 deg0 deg+22.5 deg+45 deg

MODIS Aqua VisNIR Polarization Sensitivity

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

5.0%

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Pola

rizat

ion

Sens

itivi

ty (%

)

Detector Index

VIIRS HAM A, - 8 deg SA

VIIRS HAM B, -8 deg SA

MODIS MS 1, 0 deg SA

MODIS MS 2, 0 deg SA

Polarization Sensitivity vs. Detector Index

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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.

SDR Validation

VIIRS SDR Cal/Val Team

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Organization Key Personnel

NOAA/NESDIS Center for Satellite Applications and Research (STAR)

Changyong Cao - VIIRS SDR Cal/Val Management LeadFuzhong Weng – JPSS SDR Cal/Val ChairMark Liu, Tim Chang

The Aerospace Corporation Frank De Luccia - VIIRS SDR Cal/Val Technical LeadDavid Moyer, Scott Houchin, Kameron Rausch, Christopher Florio, Jason Cardema, Evan Haas, Patrick Yuen, Allen Raines, Jeff Lipeles, Aaron Myrick, Zaven Petrosyan

NASA GSFC• NPP Instrument Characterization Support Team (NICST)• NPP Instrument Calibration and Support Element (NICSE)

Jack Xiong and Kurt Thome - Instrument ScientistsHassan Oudrari, Robert Wolfe, Robert Barnes, Gene Eplee, Fred PattNICST: Jeff McIntire (Lead), Ning Lei, Thomas Schwarting, Junqiang Sun, Alin Tolea, Shihyan Lee, Aisheng WuNICSE: Vincent Chiang (Lead), Mash Nishihama, Gary Lin

University of Wisconsin Chris Moeller

MIT Lincoln Laboratory Juliette Costa, Ed Bicknell

Northrop Grumman Airborne Systems

Lushalan Liao

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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

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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.

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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

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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

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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.

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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 Activities by Phase

L + 50 days

Early Orbit Checkout (EOC) Phase

Intensive Calibration & Validation (ICV) Phase

Pre-Launch Phase

Laun

ch

Long Term Monitoring(LTM) Phase

L + 180 days

SensorCharacterization

Performance & Telemetry Trending

Baseline

SDR Cal/ValPlan Development

SDR AlgorithmInitialization &

Update Capability

Cal/Val ToolDevelopment

FunctionalCheckout

DataInventory

RDR/SDRVerification

RadianceMatch-Ups

Geolocation

Performance &TelemetryTrending

SDR AlgorithmTuning

SDR Parameter

& LUT Updates

RadianceMatch-Ups

Geolocation

Performance &TelemetryTrending

SDR Parameter

& LUT Updates

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

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

23

MODIS Terra/AVHRR 11 m Band Comparison(Xiong et al., CEOS-IVOS 2004)

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CrIS-VIIRS Cal/Val (heritage AIRS-MODIS)

Abundant matchups on every Aqua orbit.

14 orbits per day(>10E6 matchups/day)

AIRS footprints overlain on MODIS image. Filter the sample to retain spatially uniform scenes.

Radiometric performance as function of scene temperature

Radiometric performance as function of scan mirror angle

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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• 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

Number of Control Point Matchups

Track Residuals (nadir adjusted) Scan Residuals (nadir adjusted)

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

30

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Approach based upon heritage efforts for AIRS and MODIS

SHIS, etc.on ER-2

q 20 km

705 km

MODIS on Terra/Aqua

11.01 um

Fly instrumented ER-2 along satellite track

Matching geometry of earth scene observations

Histogram of radiometric matchups

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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