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SI Traceability forSI Traceability forClimate Climate

MeasurementsMeasurements

Gerald Fraser, Carol Johnson, and Raju Datla, Joe Rice, Eric Shirley

Optical Technology DivisionNational Institute of Standards and

Technology

gerald.fraser@nist.gov

TOPICS OF INTEREST

Traceability + Traceability on Orbit

NIST Facilities- Scale realization/transfer strategy

What do YOU think?

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Reflected SolarIR Thermal Emission

Measurement of Optical Radiation & Climate

424 EarthEarth TR EarthEarthEarth SR 2

EarthEarth SR 2 REarth

Solar Constant~ 1366 W m-2

~0.30

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Climate Measurements Require a New Strategy

We need a dedicated satellite program to provide benchmark climate-quality measurements

Low uncertainties known throughout mission- provable, traceable on-orbit calibration

Benchmark measurements for future generations- an SI-traceable record is SI-traceable forever

Reference for other satellite measurement- continuity or large duty cycle is good

Instrument Digital Counts

Measurement Relative to

SI Units

f(DN,time)

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Traceability—Foundation for Accurate Measurements

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 (VIM, 6.10)

Based on the SI International System of Units

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Quality of Traceability ClaimQuality of Traceability Claim for Radiances

0

4

3

2

1

5

No Traceability

High Quality Climate Benchmark Satellites

Meteorological Satellites

Imagery Satellites

Research Satellites

Rigorously & Independently

Validated Traceability to the SI with Low

Uncertainties

No Tie to the SI & No Uncertainty Analysis

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… Instrument calibration, characterization, and stability become paramount considerations. Instruments must be tied to national and international standards such as those provided by the National Institute of Standards and Technology (NIST)...

Traceability Requirement Recognized by Climate Research Community

NIST facilities/capabilities

Presented: POWR Primary Optical Watt RadiometerSIRCUS Spectral Irradiance & Radiance Calibration

using Uniform SourcesAAMM Aperture Area Measuring MachineHIP Hyperspectral Imaging Projector

Not presented:LBIR Low-Background Infrared RadiometryRSL Remote-Sensing LaboratoryR2T Radiance & Radiance Temp., replacing

FASCAL, FASCAL2, Heat Flux FacilitySTARR BRDF facility

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LiquidHe at 2K

LiquidNitrogen

Jeanne HoustonJoe Rice

• POWR provides optical power to 0.01% (k = 2)

NIST Optical Measurements are Traceable to the Electrical Watt through

the Primary Optical Watt Radiometer (POWR)

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Tunable Laser

Wavemeter

IntegratingSphere

Exit Port

Spectrum Analyser

Lens

DetectorUnder Test

Computer

ReferenceDetector

IntensityStabilizer

Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS)

Monitor Detector (output to stabilizer)

=UV to LWIR

Chopperor

Shutter

Speckle-removalSystem

with the aid of SIRCUS

Keith LykkeSteve BrownGeorge Eppeldauer

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…and to the Meter through Aperture Area Measurements Performed by the Absolute Aperture Area Measurement Machine…

High resolution microscope

CCD camera

XY Stage Guide bar

Aperture holder

Wavelength compensator

Optics table

Granite table

Fiber optic light source Koehler illuminator

Differential plane interferometer

High resolution microscope

CCD camera

XY Stage Guide bar

Aperture holder

Wavelength compensator

Optics table

Granite table

Fiber optic light source Koehler illuminator

Differential plane interferometer

Aperture area to better than 0.01%

0 1 2 3 4 5 6 7 8 90.990

0.992

0.994

0.996

0.998

1.000

1.002

1.004

1.006

1.008

RMIB WRC ERBER

atio

Ap

ert

ure

Are

a [L

ab

/NIS

T]

Aperture Designation

Toni LitorjaJoel Fowler

Detector-based temperature realization in SIRCUS

d

Laser

Radiation Thermometer

CryogenicElectrical SubstitutionRadiometer

Si-trapDetector

PrecisionAperture

PrecisionAperture

IntegratingSphere

1

hexp

c,

52

1L

kTcnn

TL

Realization, dissemination of temperaturescales above Ag freezing point

Scene viewed by a typical optical sensor instrument

Scene viewed by anImaging instrument

In practice

Consider the complexity of real-world scenes:

Hyperspectral Imaging Projector (HIP)

Digital Micromirror Device (DMD)

• An array of MEMS micromirror elements

• Commercially available:• 1024 x 768 elements • Aluminum mirrors• 13.7 micron pitch

• For visible to 2500 nm applications:commercially available

hardware

• For longer wavelength infrared developments we are using DMDs where the glass window is replaced by a ZnSe window.

• Control algorithms are being written using everyday control software for everyday hardware interfaces and operating systems.

Digital Light Processing (DLP) Projectors

Reference: www.dlp.com

Hyperspectral Image Projector (HIP) Prototype

L6

DMD1

Illumination Optics

Homogenizer

ProjectionScreen

Fold MirrorProjection

Optics

DMD2

Beam Stop 2

Spatial Engine

Unit Under Test (UUT)(or Reference Instrument)

Spectral EngineBand M

Spectral Image

Band MSpatial Image

Beam Stop 1

L3

M1

Prism2

Prism1L4

L2

L1SupercontinuumFiber Laser

L5-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

450 500 550 600 650

Rel

ativ

e In

tens

ity

Wavelength (nm)

Can substitute with other foreoptics to present to UUT

How the DMD is used to create an arbitrarily programmable spectrum

Breadboard HIP

Top View

View of Source input to Spectral Engine

Spectral DMD

Spatial DMD

Prism 1

Prism 2

FLOW OF LIGHT(source not shown)

Example image as projected by the prototype HIPonto a white screen and taken using a digital camera

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Climate Measurements Require a New Strategy

We need a dedicated satellite program to provide benchmark climate-quality measurements

Low uncertainties known throughout mission- provable, traceable on-orbit calibration

Benchmark measurements for future generations- an SI-traceable record is SI-traceable forever

Reference for other satellite measurement- continuity or large duty cycle is good

Instrument Digital Counts

Measurement Relative to

SI Units

f(DN,time)

EXTRASLIDES

FOLLOW

• Utilizes non-linear effects in a photonic crystal optical fiber to greatly broaden the spectrum of a 1064 nm pump laser.

Four-wave mixing:

• Broadband light is generated in a single-mode (5 micrometer core diameter) photonic crystal (holey) optical fiber

– No etendue issues as with lamps or blackbodies. Light is all “born in the same place”good for control.

– Ideally suited for coupling to a spectral engine.

• High power and high spectral resolution:

– 3 mW/nm spectral power density from 450 nm to 1700 nm

• Commercially available.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

500 1000 1500 2000 2500

SC450 ASD

Po

we

r (a

rbitra

ry u

nits)

Wavelength (nm)

Supercontinuum Fiber Laser: A “White” Broadband Laser

)()( hhhh

Comparison of Matched Spectra: Xe Lamp vs Supercontinuum

0.0

0.2

0.4

0.6

0.8

1.0

450 500 550 600 650 700

EM4: Xe Prism SE, Vegetation EMR

ela

tive

Inte

nstit

y

Wavelength (nm)

Target

Measured

Difference

0.0

0.2

0.4

0.6

0.8

1.0

450 500 550 600 650 700 750 800 850

EM7a

Rel

ativ

e In

tens

tity

Wavelength (nm)

Target

Measured

Difference

With Xe Lamp, Vegetation Spectrum

Spectral Images(on DMD)

With Supercontinuum Fiber Laser

Input Image Cube

Example: AVIRIS image cube of on San Diego N.A.S.

Based on using ENVI/SMACC to find these endmember spectra / abundances

J. Gruninger, A. J. Ratkowski, and M. L. Hoke, “The sequential maximum angle convex cone (SMACC) endmember model,” Proc. SPIE 5425, 1-14 (2004).

EM-3

EM-4

EM-2 EM-5

EM-6

Endmember Abundances

EM-1

EM-1

Endmember Spectra

EM-2

EM-3

EM-5

EM-4

EM-6EM-7

Then we need only project N = 6 broadband spectra instead of M = 30+ monochromatic spectra.

Endmember decomposition