VIIRS GSFC Ocean Science Team Report and Assessment (OBPG) · spectral response, “intra-band” crosstalk is indistinguishable from directly transmitted (non-scattered) out-of-band

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VIIRS GSFC Ocean Science Team Reportand

Ocean ColorEnvironment Data Record (EDR)

Assessment

K.Turpie(OBPG)

MODIS/VIIRS Science Team Meeting26-28 January 2010 - Washington, D.C.

Final version

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VIIRS GSFC Ocean Team ReportCurrent NPP CDR ShowstoppersRisksInstrument Performance:- NPP VIIRS Radiometric Performance- NPP VIIRS Spectral PerformanceEDR Assessment (Modeling Crosstalk)EDR Assessment (Out-of-Band Light leaks)SummaryBackup Slides

CONTENTS

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101416303742

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VIIRS GSFC OCEAN TEAMREPORT

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CALIBRATION MANEUVERS ARE NOT YET APPROVED• Lunar roll maneuvers are a minimum requirement for NASA data continuity; needed totrack trends in detector degradation during the mission.• Yaw maneuver is required to characterize calibration system on-orbit only once or twiceduring the mission.• [One-time pitch-over maneuver is also necessary to characterize RVS for SST.]

THERE IS NO MISSION-LEVEL REPROCESSINGThere is no support for the application of vicarious gain across the entire data record, or toaddress on-orbit anomalies, or to address major algorithm changes. Mission-levelreprocessing is a critical minimum requirement for a climate data record or to meetingproduct performance specifications.

ALGORITHMS ARE OUTDATED AND INCONSISTENTCurrent operational NPP algorithms are inconsistent with NASA climate data record.Atmospheric correction is missing several years of development. Chl-a algorithm wasdemonstrated to perform more poorly than current NASA selected algorithm.

CURRENT NPP CDR SHOWSTOPPERS

These are currently unresolved, and preclude NPP fromproducing ocean color climate data records (CDR).

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Crosstalk - Optical crosstalk could have a significant impact onocean color data quality. Polarization sensitivity, electronic crosstalk, andother uncertainty sources hamper characterization.

Out-of-Band Response - Larger than MODIS light leakshave be found in VIIRS; especially high in 412 & 551nm channels.

Spectral Characterization Uncertainty -characterization of crosstalk and out-of-band response show signs ofsignificant uncertainty, which could hamper on-orbit correction. There isa plan for NIST to test spectral response at S/C level with SIRCUS.

SNR - Signal-to-noise ratio is comparable, but lower than MODIS inthe 3:1 agg zone, but drops at higher scan angles. Impact to coverageneeds to be evaluated.

Gain switch anomaly - at ~90% gain switch point, VIIRS hasincreased non-linearity and noise. Note that detectors do not switch atthe same radiance (0-20% of Lmax(HG)). M1 was observed switchingbelow the Lmax(HG) switch point, but red light leak may have pushed gaintransition low in lab.

RISKS: Instrument Performance

ModerateRisk

LowRisk

HighRisk*

* Risks to meeting NASA’s data continuity requirements.

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System Level Calibrator Test - RSB Calibrator systemremains untested and considered at high risk. There is a plan for NISTto test calibrator at S/C level with SIRCUS.

Calibration Packets for band M4 & M5 -Calibration packets were being substitute by DNB data during calibration,but this has been remedied. This was verified in FP-18 Day-in-the-Lifetesting data. It was noted however that transition between day and nightmode is staggered over at least three scans.

SDSM misalignment - SDSM was manufactured with wrongorientation; may reduce number of measurements of the sun withcharacterized portion of SDSM screen.

HighRiskRESOLVED

LowRisk

HighRiskREDUCED

RISKS: Calibration System

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Vicarious Calibration Infrastructure Support -Potential assets and resources identified in IPO Ocean Cal/Val Plan:future support not completely clear.

Validation Data Collection - Tasks and potentialresources are identified in the IPO Ocean Cal/Val Plan. NASA SeaBASSpossible repository for data. Are enough resources adequatelysupported?

OC Calibration Analysis Team - To meet minimumrequirements it is critical to have a dedicated team to evaluate calibrationdata, including vicarious and lunar calibration data, and handle instrumentcalibration trends or anomalies. Personnel are identified in IPO OceanCal/Val Plan, but agency agreements are not in place.

Independent Assessment Team - An independentteam to evaluate data quality is recommended. Tasks and personnel areidentified in the IPO Ocean Cal/Val Plan, but agency agreements are notin place.

Recommendation: Perform gap analysis for Cal/Val resources andassets, in context of what is now known about VIIRS performance.

ModerateRisk

HighRisk

ModerateRisk

ModerateRisk

RISKS: Postlaunch Activities

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Algorithm Change Pathway Long and Slow -There are too many decision gates to approve algorithm changes.Working with the ocean color community for algorithm development islikely to be hampered.

ModerateRisk

RISKS: Postlaunch Activities

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INSTRUMENTPERFORMANCE

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comparable to MODIS, better than SeaWiFS. M7does not pass EOL specification.

Near-field Response

Meets spec with large margin (50-100%)Stray Light

Meets requirements.Response Verses Scan

Within 0.3% over one orbit for bus voltage,temperature.

Stability

Only the NIR (748 & 865nm) bands pass spec forgain uniformity.

Uniformity

Linearity < 0.15% for ocean bands.Characterization Uncertainty in spec.

Linearity

M1 (412nm) and M8 (1240nm) thought to switchgain lower than expected, but M1 probably due tored light leak artifact.

Dynamic Range

12 bits. (+1 for dual gain bands)Resolution

Systematic noise spikes, esp. blue bands (M1-3),~3:10-6 freq.

Noise

< MODIS in visible bands, best in 3:1 agg zone,high in NIR

Signal-to-Noise Ratio

< MODIS, better characterizedPolarization SensitivityNPP VIIRS Radiometric Performance

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Dual-gain Bands - samples aggregated on ground.Singe-gain Bands - samples aggregated on-board (only M6 for ocean bands).

source: MDFCB, 4 Nov 2004

1 2 356o 43.6o 32o 32o 43.6o 56onadir

1500km 850km 530km 530km 850km 1500kmScan Aggregation Zones

SNR@Ltyp by Aggregation Zone

4 5 6

880838

803750

914

600

517

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• During EDU, anomalies in various tests were observed that were traced backto communication between band detectors.

• Three main types crosstalk were identified (other flavors exist of much lessconcern):

• Optical• Static Electronic• Dynamic Electronic

• Optical crosstalk is claimed to be an order of magnitude larger than staticelectronic crosstalk and has been considered the main concern.

• Dynamic crosstalk was greatly reduced by adding bonding wires to the focalplane assembly and is only expected to produce an effect along edges of verybright targets.

• In addition, a strong out-of-band response was discovered in FU1 duringspectral response characterization.

NPP VIIRS Spectral Performance

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Polarization angle = 6°

570nm light

Based on 5-10 second exposure photos by Pete Fuqua (Aerospace Corp.)Feb 11, 2009

M4 filter

Hyperbolic Cut

Circular Cut

551nm light

Incoming LinearlyPolarized Light

Polarization angle = 6°

• Scatter centers in filter direct light atspecific out-of-band wavelengths to exitthe filter in high-angle cones.

• In the scan direction, this extraneousout-of-band light is transmitted to otherbands as “inter-band” optical crosstalk.

• In the track direction, the sameproduces out-of-band stray light thathas been called “intra-band” crosstalk.

• In the principal tests to characterizespectral response, “intra-band”crosstalk is indistinguishable fromdirectly transmitted (non-scattered) out-of-band leakage.

• Polarization causes exiting light toform lobes in the direction of the Evector.

FILTER LEAKS IN NPP VIIRS

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EDR ASSESSMENT(Modeling Crosstalk)

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NPP VIIRS Crosstalk Impact Assessment• Work by Northrop Grumman, Raytheon, MIT LincolnLabs, Aerospace and NASA have contributed over threeyears to understanding crosstalk in VIIRS, leading to amodel heavily based on characterization data.

• As a numerical experiment, this model was extended topredict the result if MODIS had crosstalk similar to VIIRS.

• Unlike previous exercises that focused on the worst casescenario, this current experiment excludes the out-of-bandinfluence in the crosstalk model.

• Out-of-band effects are more difficult to evaluate sincetheir characterization are an integral part of the oceancolor algorithm.

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NPP VIIRS Crosstalk Impact AssessmentLIMITATIONSThe current model and this analysis of the results areentirely preliminary (caveat emptor!).There are many sources of uncertainty that have notbeen bounded.

In modeling VIIRS crosstalk in MODIS :

• A crude model of point-to-point propagation is applied,• Interpolation and weighting schemes are used to map toand between MODIS bands, and• Electronic crosstalk is not included in the modeling.

Also, further stratification of results will be needed toassess impact to specific science questions.

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ATMFAILLANDCLDICEHILTSTRAYLIGHT

HISATZENCOCCOLITHLOWLWCHLFAILCHLWARN

NAVWARNMAXAERITERATMWARNHISOLZENNAVFAIL

FILTERSSTWARNSSTFAILHIGLINT

Atmospheric correction failure Pixel is over landProbable cloud or ice contaminationTOA radiance is highStraylight contamination is likely

satellite zenith threshold < 60 degreeCoccolithofores detectedVery low water-leaving radiance (cloud shadow)Derived product algorithm failureDerived product quality is reduced

Bad navigationAerosol iterations exceeded maxAtmospheric correction failureHigh solar zenithBad navigation

Pixel rejected by user-defined filterSST quality is reducedSST quality is badHigh sun glint

L2 Flags used to select high quality pixels

RED - Flags used for coastal scenes with fewer ideal pixels

200 pixels trimmed fromswath edge to removebow tie effect.

NPP VIIRS Crosstalk Impact Assessment

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A20031711810Argentina, 20 June 2003

A20040332355Hawaii, 2 February 2004

A20051071815East USA, 17 April 2005

Three scenes were selected: one open ocean near the vicarious calibration site andthe other two with coastal and in-land waters.

Special thanks to NICST for all their hard work in creating these modeled scenes.

NPP VIIRS Crosstalk Impact Assessment

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Region Bias and Variation Summary StatsNPP VIIRS Crosstalk Impact Assessment

869 and 443nm bands show the most effect for TOA radiance. Other bands show tolerablelevels of crosstalk impact.

Based on current data, optical crosstalk alone produces a modest, but significant impact toocean color products - but less than previous worst case scenarios.

NASA algorithm is more resilient to crosstalk than the operational NPP alogorithm whichappear to be devastated by this effect.

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Region Bias and Variation Summary Stats

]

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EDR ASSESSMENT (Out-of-Band Light Leaks)

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NPP VIIRS FU1 has a much larger out-of-band responsethan EDU (or MODIS).

* Waiver threshold

Requirement

* NICST now predicts a value comparable to the other teams for M5.

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NPP VIIRS Spectral PerformanceNPP VIIRS FU1 results have yielded significantdifferences between detectors and between analysisteams.

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Taking the differences of the radiometric errors from theOOB response when measuring a blue ocean and thesolar diffuser provide an estimate of the reflectance error.

Ecal for Blue Ocean

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SUMMARY

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SUMMARYNPP VIIRS RISKS:

• NPP VIIRS simply cannot produce science or climate qualityocean color data without 1) reprocessing, 2) maneuvers, and3) current NASA selected and developed algorithms.

• A gap analysis is recommended for Cal/Val resources and assetsin the context of what is now known about VIIRS performance;agency agreements need to be in place for IPO Cal/Val plan to besuccessful.

• VIIRS spectral response and crosstalk issues remain a majorconcern, especially regarding uncertainty and whether any on-orbitcorrection will be viable.

• VIIRS radiometric performance would otherwise be good, barringconcern for moderate SNRs and possible striping.

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CROSSTALK EDR ASSESSMENT:

Very preliminary, crosstalk model, based on the latest data, wasapplied to three MODIS scenes (one open ocean, two with coastaland in-land waters).

RESULTS

• Impact is smaller without out-of-band, but significant crosstalk wasstill produced in the 443nm and 869nm channels of the MODIS data(~0.3% and ~0.4%, respectively, for TOA radiance).

• Normalized water-leaving radiance and Chl-a showed regionalbiases and variation that often met NPP EDR performancerequirements, but consumed a large amount of the error budget.

• Data products for coastal and in-land water had the greatest impact.

• NASA Chl-a algorithm (OCM3) was more robust in the presence ofcrosstalk than the NPP operation algorithm, especially in coastalwaters.

SUMMARY

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OUT-OF-BAND LIGHT LEAK:

• A significant out-of-band response was found in the FU1spectral characterization.

• Only the 443nm and 865nm channels remain clearly withinspecifications; all other ocean bands fail spec.

• It is not clear, given the currently poorly bounded uncertainties,whether conventional methods of correction would be adequate.

• Further study of correction method’s efficaciousness will beneeded to complete EDR assessment.

Uncertainty and complexity in the characterization/modelingof crosstalk and out-of-band response are of great concern.

SUMMARY

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PATH FORWARD:

• Determine an upper bound for uncertainty in the effects ofcrosstalk and out-of-band response.

• NIST SIRCUS might assist in quantify some of the net uncertainty.

• Assess the viability of existing out-of-band correction schemesgiven magnitude and uncertainty of the behavior.

• Evaluate techniques to mitigate crosstalk effects, givenuncertainty.

• Assess performance on-orbit in context of what was learnedprelaunch.

SUMMARY

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BACKUP SLIDES

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SNRPerformance

From Junqiang Sun (NICST), 25 Jan 2010. VIIRS F1 Pre-Launch Calibration and Characterization: Reflective Solar Band Radiometry, slide 19.

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UniformityPerformance

There are detectors in all bands except M6-M7, which do not satisfy the specification

From Junqiang Sun (NICST), 25 Jan 2010. VIIRS F1 Pre-Launch Calibration and Characterization: Reflective Solar Band Radiometry, slide 26.

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A20051071815 - East USA 17 April 2005Blow-up of DelMarVa Penninsula Region

The East USA scene was specificallyselected to look at particular geographicregions. The above inset shows theneritic Atlantic waters that are fed by theChesapeake and Delaware bays.Differences in response between turbidand clearer water can be seen.

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Region Bias and Variation Stratified by Value

All FlagsUsed

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• Test Configuration:! Detector-to-detector differences were observed, possibly fromslit alignment and non-uniformity in source along track.! Bulb instability was possibly observed, especially in towardthe blue end; there has been resistance to further evaluation.! Bulb used to measure 865nm band (M7) burnt out before itwas properly characterized.! TVAC chamber window characterization.

• Polarization:! Source is polarized; VIIRS crosstalk and OOB RSR arepolarization sensitive.! Degree of Polarization can be high for crosstalk, moderate forRSR OOB.! Polarization uniformity along track of source not verified.! Polarization response of crosstalk was measured for only afew wavelengths, for a few bands, at only for polarization angles.

NOTES ON SOURCES OF UNCERTAINTY FOR OCEAN BANDS:

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• Point-to-point Propagation:! Tests only characterized a fully illuminated filter and may nottranslate well to partial illumination from spatial structure inimage.! Point-to-point propagation of light from is roughly known andbehavior is not completely consistent from band to band,detector to detector, or wavelength to wavelength.! Current point-to-point model predicts striping from crosstalk.! Maybe impossible or infeasible to model point-to-pointpropagation on orbit to remove striping.


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• Measurement and Processing Error:! Measurement noise (inc. dark count); repeatability has beendemonstrated to be poor.! Biases from stitching together in-band and out-of-band datasets.! Electronic crosstalk could produce an addition uncertainty inoptical crosstalk characterization and on-orbit correction.! 1nm uncertainty in wavelength calibration could also introducebiases. May also be smile uncertainty along track.


NIST is expected to use SIRCUS to characterizethe VIIRS spectral response after the instrumentis integrated on the spacecraft.

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Documents

VIIRS GSFC Ocean Science Team Report and Assessment (OBPG) · spectral response, “intra-band” crosstalk is indistinguishable from directly transmitted (non-scattered) out-of-band