CLARREO: Radiometric Concept and Requirements John A. Dykema, P. Jonathan Gero, Stephen S. Leroy, James G. Andeson Harvard University Major contributions:

CLARREO: Radiometric Concept and RequirementsJohn A. Dykema, P. Jonathan Gero, Stephen S. Leroy, James G. AndesonHarvard University

Major contributions: University of Wisconsin (SSEC)National Institutes of Standards and Technology

Dykema et al.: CLARREO Radiometric Concept and ...

Important Sub-fields Related to High Accuracy Long-term Climate RecordsSI traceable standardsTechnology and strategy for establishing absolute scalesInnovation for detection of systematic errorsAtomic clocks, phase transition cells, frequency stabilized lasersAccuracy, precision and bias on-orbitBlackbodies, frequency standards, temperature cellsQuantum cascade lasers, linear detectors, polarization of optical systems in spaceTargets for calibration: Moon, stars, etc.Ground-based observationsSondes, GEOSUse of weather data for climateIntercomparison methods between satellitesIn-situ intercomparisonsMetrologyOptical Systems for High Accuracy Observations from SpaceClimate Community and Climate RecordsNISTASIC3IPCC, GEOSS


NIST Standards to Tie On-orbit Measurements to International StandardsSource: Sergey Mekhontsev, NIST


Keeling curveMonthly mean CO2 concentration at Mauna Loa, HawaiiObservations started by C. D. Keeling in 1958NOAA Global Monitoring Division

Figure 14 The 28-year Total Solar Irradiance record comes from several overlapping instruments. Offsets are due to inconsistent absolute accuracies, although each instrument precisely monitors short-term TSI changes. None of these instruments is calibrated end-to-end for irradiance at the desired absolute accuracy levels, as no such facility currently exists. The error bar shown indicates 0.1 % variation.


Current Measurements Inhibit Application of the Scientific Method


Requirements0.1 K at 750 cm-1 and 250 K target (3-s)Far-IR to near-IR (100-200 cm-1 to 2500-3300 cm-1)1 cm path difference (~0.6 cm-1) resolution


Achieving SI traceabilityThe SI traceability of a radiometric measurement may be determined only when multiple (redundant) SI traceable standards are available:Pollock, D. B., T. L. Murdock, R. U. Datla, and A. Thompson, Data uncertainty traced to SI units. Results reported in the International System of Units, International Journal of Remote Sensing, 24(2), 225-235, 2003.

Previous SI standards based on well-founded physical principles were subject to irreconcilable drifts; for example, electrochemical cells for the standard volt, revealed only by quantum electrical standards.- Hartland, A., Quantum Standards for Electrical Units, Contemporary Physics, 29(5), 477-498, 1988.


The Foundations of the Infrared SI ScaleMartin, J. E., and P. R. Haycocks, Design considerations for the construction of an absolute radiation detector at the NPL, Metrologia, 35(4), 229-233, 1998. Quinn, T. J., and J. E. Martin, A Radiometric Determination of the Stefan-Boltzmann Constant and Thermodynamic Temperatures between -40 C and +100 C, Philosophical Transactions of the Royal Society of London Series A- Mathematical, Physical and Engineering Sciences, 316(1536), 85-160, 1985.Quantifying Systematic Uncertainties On-OrbitASIC-3 report: If an observation is not initially SI traceable against an absolute scale, it cannot engage in the logic of testing for systematic error.


Tracing the on-orbit calibration to primary standards1.2.Detectorbased


Spectral Infrared Measurements Achieve Traceability via Plancks Law


Temperature calibration: thermodynamic, practicalThe Kelvin: 1/273.16 of the triple point of waterITS-90: fixed points define scale relevant to thermal infrared


Measurement of EmissivityExperimental setupMeasurement of emissivity experimental setupBlackbody surfaces characterized with reflectometerLight source: 8um quantum cascade laser with integrating sphere (Labsphere)Measurements calibrated with a traceable reference standard

Far IR Properties of CoatingsFrom Persky and Blue 1992


Uncertainty (Error) Budget for Infrared


SI Temperature On-Orbit: Integration of Phase Transition Cell with Blackbody


Determination ofEmissivity On Orbit: Quantum Cascade Laser


Determination of Emissivity On Orbit: Heated Scene Tube


End-to-End Sensor Evaluation


The Multiple Interferometer


ConclusionsNIST involvement at every step:Intellectual FrameworkMaterials CharacterizationSubsystem TestingFull Sensor Evaluation


Supporting Materials


Diurnal and Semidiurnal Cycles


Diurnal Cycle, Window (909 cm-1)GFDL CM2.0, fully coupled


Semidiurnal Cycle, Window (909 cm-1)GFDL CM2.0, fully coupled


Semidiurnal Cycle (909 cm-1)GOES & TOVS, 3-hourly analysisSalby et al. (1991)


Comparison of 90 Polar Orbit, Sun-Synchronous Orbit, Low-Latitude Precessing Orbit


Spectral Diurnal Cycle


Spectral Semidiurnal Cycle


Instrument Line Shape and Spectral Response Function On Orbit: Quantum Cascade Laser and Atmospheric Rotation-Vibration Lines


Historical CO2 data 3Historical CO2 DataSlocum, 1955NOAA Global Monitoring Division

GPS RO: a climate index tied to the atomic clock


Calibration: Double DifferencingHardy, K.R., G.A. Hajj, and E.R. Kursinski, 1994: Accuracies of atmospheric profiles obtained from GPS occultations. Int. J. Sat. Comm., 12, 463-473.


Achieving SI traceabilityThe SI traceability of a radiometric measurement may be determined only when multiple (redundant) SI traceable standards are available:Pollock, D. B., T. L. Murdock, R. U. Datla, and A. Thompson, Data uncertainty traced to SI units. Results reported in the International System of Units, International Journal of Remote Sensing, 24(2), 225-235, 2003.

Previous SI standards based on well-founded physical principles were subject to irreconcilable drifts; for example, electrochemical cells for the standard volt, revealed only by quantum electrical standards.- Hartland, A., Quantum Standards for Electrical Units, Contemporary Physics, 29(5), 477-498, 1988.


NPLs cell voltage transfer standardNISTs Josephson voltage standard


HgCdTe


Chart5

19.7989172467

14.9446205392

10.0504141743

7.5853736867

6.0983256653

5.1019988315

4.3866941661

3.8472815388

3.4252487794

3.085444416

2.8054806422

2.5704249804

2.3699377222

2.1966341895

2.0451010758

1.9112811055

1.7920745503

1.6850733754

1.5883792127

1.5004758566

1.4201381313

1.346365573

1.2783333832

1.2153556263

1.156857248

1.1023525448

1.0514284164

1.0037312089

0.9589562844

0.9168396832

0.8771514084

0.8396899783

0.8042779805

0.7707584201

CdTe mole fraction (Hg1-xCdxTe)

Cutoff wavelength (mm)

Sheet1

0.18750.062629687519.7989172467

0.20.08297314.9446205392

0.2250.12337810.0504141743

0.250.16347257.5853736867

0.2750.20333456.0983256653

0.30.2430425.1019988315

0.3250.2826734.3866941661

0.350.32230553.8472815388

0.3750.36201753.4252487794

0.40.4018873.085444416

0.4250.4419922.8054806422

0.450.48241052.5704249804

0.4750.52322052.3699377222

0.50.56452.1966341895

0.5250.6063272.0451010758

0.550.64877951.9112811055

0.5750.69193551.7920745503

0.60.7358731.6850733754

0.6250.780671.5883792127

0.650.82640451.5004758566

0.6750.87315451.4201381313

0.70.9209981.346365573

0.7250.9700131.2783333832

0.751.02027751.2153556263

0.7751.07186951.156857248

0.81.1248671.1023525448

0.8251.1793481.0514284164

0.851.23539051.0037312089

0.8751.29307250.9589562844

0.91.3524720.9168396832

0.9251.4136670.8771514084

0.951.47673550.8396899783

0.9751.54175550.8042779805

11.6088050.7707584201

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CdTe mole fraction

Cutoff wavelength (micron)

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CdTe mole fraction (Hg1-xCdxTe)

Cutoff wavelength (mm)

Sheet3

Temperature calibration: thermodynamic, practicalThe Kelvin: 1/273.16 of the triple point of waterITS-90: fixed points define scale relevant to thermal infraredStandard Platinum Resistance Thermometer (SPRT): interpolates between fixed points


Why SI traceability?NRC DS:high accuracy, tested for systematic errors on-orbit, and tied to irrefutable standards


What is the SI?Units defined by fundamental properties of matterWell-established uncertainty estimatesWell-explored relationships to fundamental constants


FIG. 10. Results of the satellite merging calculation analogous for the NOAA-11NOAA-12 overlap period. The gray dots are the NOAA-11NOAA-12 differences. The black dots represent the fit to the differences using the ocean-only target multipliers. The black crosses are the after-the-fit residuals, offset so that the horizontal line is zero. (a) Merger performed without the diurnal correction. Note the overall slope of the residuals in the 199295 time period due to the drift in local crossing time of NOAA-11. (b) Merger performed using the diurnal correction. Note the marked reduction in the slope and the seasonal cycle in the residuals. This provides another check on the validity of the CCM3-based diurnal correction.


What is traceability?Standard definition: the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.Easy enough: what constitutes unbroken?


Quantifying the SI traceability of an infrared remote sensing measurementRice, J. P., and B. C. Johnson, NIST activities in support of space-based radiometric remote sensing, Proceedings of the SPIE - The International Society for Optical Engineering, 4450, 2001.Tsai, B. K., and B. C. Johnson, Evaluation of uncertainties in fundamental radiometric measurements, Metrologia, 35(4), 587-593, 1998.

Step 1: Start with Calibration Equation


Calibration equation includes complex phase (Revercomb et al. 1988) information:The measured signal is a vector sum of the two input ports plus beamsplitter emission:The input radiance includes scene radiance plus self-emission from the optics:These equations allow for completely general phase relationships appropriate to an absorbing, single-layered beamsplitter (Weddigen, Thriault).


Stray light effects cannot be ignored:Nor can polarization effects:Note that nonlinearity aliases spectral information and is best expressed in the interfogram (temporal) domain:


Errors due to a detector nonlinearity of a=0.01


Detector Design: Linearity, Stability, Simplicity, Stray Light RejectionLinearity is first priority for high accuracySource of error for quantum detectors:Carrier mobility decreased by high carrier concentrationFree-carrier effects alter surface reflectivityCarrier lifetime reduced by higher recombination ratesPhotovoltaic detectors improve linearity over photoconductive casePyroelectric detectors are strong choice, since they are inherently linear for thermal fluxesStray light rejection:Pyroelectric detectors generate signal only in response to modulated radiationDetector areaPyroelectric coefficient


Stray light errors occur only for changing ambient radiation conditions They are most pronounced for scene temperatures with strong constrast to ambient temperature


ConclusionsFoundation: calibration standards with clear path to SIKey lessons from practice of metrology: - different physical pathways to the same measurement goals- redundant measurement standards to quantify level of accuracy achievedElectrology: quantum vs. electrochemicalIR radiometry: source vs. detector based methodsTesting for systematic uncertainties on-orbit for IR CLARREO- Basis is blackbodies with independent means of on-orbit assessment- Utilize calibration equation and independent measurement physics to analyze end-to-end (combined) uncertainty


Documents

CLARREO: Radiometric Concept and Requirements John A. Dykema, P. Jonathan Gero, Stephen S. Leroy, James G. Andeson Harvard University Major contributions: