1 si traceability for climate measurements gerald fraser, carol johnson, and raju datla, joe rice,...
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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
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.
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