Capabilities of NIST SIRCUS for
Calibrations of SSI Vis-IR
Instruments
Steve Brown
National Institute of Standards & Technology
Gaithersburg, MD
steve.brown@nist.gov; 301.975.5167
Answer: Ask LASP folks
In 2005/2006, SIRCUS measured a SIM brassboard slit scatter function & ESR responsivity with
Erik Richard, Jerry Harder and Colleagues from Laboratory for Atmospheric and Space Physics
(LASP), Boulder CO
•
Spectral Irradiance Monitor (SIM) on SORCE
– SIM is a Fèry prism spectrometer; only one optical element is needed to disperse and focus
the light onto four photodiode detectors and an electrical substitution radiometer (ESR).
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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SIM Brassboard Slit Scatter Function
Grey lines – ray trace model
J. W. Harder, G. Thuillier, E. C Richard, et al., “The SORCE SIM Solar Spectrum
Comparison with recent observations,” Solar Phys. 263, 3-24 (2010).
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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ESR Efficiency Results
Net result was that the radiometric response of the SIM instrument
needs to be increased by a factor of 1.013 across the 258 nm to 1350 nm regime.
J. W. Harder, G. Thuillier, E. C Richard, et al., “The SORCE SIM Solar Spectrum
Comparison with recent observations,” Solar Phys. 263, 3-24 (2010).
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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SSI Workshop 1, September 2006
Worthwhile repeating the measurements
Solution: NIST loaned LASP an L-1 Stnds&Technol cryogenic radiometer and a
Traveling SIRCUS system
Contact: Dave Harber, LASP, dave.harber@lasp.colorado.edu
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
5
NIST SIRCUS Capabilities for SSI Measurements
in the Reflected Solar Regime
• Introduction to SIRCUS
• What do we need the facility to do?
– Available irradiance
– Uncertainty requirements
• Can SIRCUS achieve irradiance levels and
uncertainties required for SSI climate change
sensors?
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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Facility for Spectral Irradiance and Radiance
responsivity Calibrations using Uniform Sources
• Develop broadly tunable laser
systems to replace
– Fixed frequency laser systems for scale
derivations
– Lamp-monochromator systems for
detector calibrations
NIST Radiant Flux (Power) Uncertainties
— Extend the spectral region of low uncertainty;
— Extend to irradiance and radiance responsivity
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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Coupling Tunable Lasers with Cryogenic Radiometers
Scale Derivations
Historically QE measured at a few
points and interpolated using a physical
model developed at NIST
1.00
0.995
With SIRCUS, we can
1. directly measure and fit the
quantum efficiency of Si trap
detectors
2. extend the spectral coverage
beyond the Si region
0.985
0.980
0.975
400
500
600
700
800
900
1000
λ [nm]
1.00
0.995
0.990
EQE
• Developed for the 405 nm to
920 nm spectral region
• Uncertainties tend to be
much larger outside this
spectral region
ηe
0.990
0.985
0.980
0.975
0.970
0.965
0.960
300
400
500
600
700
800
900
1000
Wavelength (nm)
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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SIRCUS
• Lasers determine the spectral coverage
• Detectors determine the uncertainties
ultimately achievable
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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Does SIRCUS provide enough Irradiance?
Optical Power: Lasers v. Lamp Monochromator Systems
SIRCUS
NIST Lamp-Monochromator
Monochromator Output Flux (Power) [µW]
10
Argon Mini-Arc
420 nm
100 W Q uartz-Halogen Lamp
1270 nm
1
985 nm
600 nm
840 nm
0.1
1385 nm
0.01
200
400
600
800
1000
1200
1400
1600
1800
Wavelength (nm)
1000 mW
1 µW
SIRCUS: 106 times more power
2012 February
Solar Spectral Irradiance (SSI) Variations
Workshop
10
Does SIRCUS provide enough Irradiance?
SIRCUS irradiance levels (in a 2 inch beam) compared with
solar levels (in a 10 nm bandpass)
E-490 (10 nm bp) v SIRCUS (5 cm diameter beam)
1.E+04
Irradiance /(W/m 2)
1.E+03
Linear Plot ETR ASTM E-490 vs. Wehrli WMO
-2
Spectral Irradiance W*m *micron
-1
2200
2000
1800
1600
1.E+02
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1400
1200
1.E-04
200
1000
800
400
600
800
1000
1200
600
Wavelength /nm
400
200
0
0
0.5
1
1.5
2
2.5
3
3.5
4
Wavelength micrometers
2012 February
Solar Spectral Irradiance (SSI) Variations
Workshop
11
Can SIRCUS achieve the required uncertainty?
How are the uncertainties validated?
SSI Uncertainty Requirements for Climate Studies
NPOESS SIM instrument: relative uncertainty of 0.01 % and a combined absolute
Uncertainty of < 0.5 % from 200 nm to 2400 nm.
Erik Richard, et al.
TRUTHS Requirements for SSI: < 0.1 % (k=1)
CLARREO: solar reflected radiation 0.3 % (k=2)
SIRCUS Propagated Uncertainties (Si region)
0.075 % (k=2)
Reference Detector
Laser
2012 February
V
Solar Spectral Irradiance (SSI) Variations
Workshop
Distance
Aperture Area
Uniformity

exit port (radiance)

ref plane (irradiance)
Detector Responsivity
I-V Gain factor
12
Validating SIRCUS Uncertainties
Development of Imaging Radiometers
Howard Yoon, David Allan, & colleagues, NIST
Gold-point
Blackbody
2012 February
Advanced Pyrometer 1
Solar Spectral Irradiance (SSI) Variations
Workshop
13
Radiance Responsivity of the Absolute Pyrometer 1 (AP1) and
Spectral Radiance from the Gold-Point Blackbody
10-4
10-4
1337.33 K
-6
Spectral Radiance, L [ W/(cm2sr) nm ]
Radiance Responsivity, SL [ A/W/(cm2sr) ]
S ( A ) = ∫ LPlanck ( λ , T )R ( λ ) d λ
10
10-6
10-8
10-8
10-10
10-10
10-12
10-12
10-14
400
10-14
500
600
700
800
900
1000
Wavelength [ nm ]
Howard Yoon, NIST
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
14
Melting and Freezing Cycles of the
Gold-point Blackbody
1370
1360
TAP1 [ K ]
1350
1340
1330
AP-1
Measurements
1320
0
200
400
600 800 1000 1200 1400
Time [ min ]
Howard Yoon, NIST
2012 February
Solar Spectral Irradiance (SSI) Variations
Workshop
15
Temperature Determination of a
Gold-point Blackbody Source
Radiometric
1337.33 K
1337.54 K
-10
1.007x10
Photocurrent [ A ]
1.006x10-10
1.005x10-10
1.004x10-10
1.003x10-10
1.002x10-10
1.001x10-10
1.000x10-10
9.990x10-11
1337.1 1337.2 1337.3 1337.4 1337.5 1337.6 1337.7
0.15 % (k=2) in Radiance Resp.
120 mK
T90
T
Temperature [ K ]
H. Yoon, NIST
T90=International Temperature Scale of 1990
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
16
Conclusions
• SIRCUS has both the flux levels and the uncertainties (from
210 nm to 1.6 µm) required to support characterization and
calibration of Solar Spectral Irradiance sensors
• Demonstrated success looking at a SIM Breadboard
instrument at NIST and work currently underway at LASP
Acknowledge: SIRCUS Personnel
• Keith Lykke, Leader
• SIRCUS Staff
– Steve Brown, Ping Shaw, Allan Smith
• Contributors
– George Eppeldauer, Transfer Standard Detectors
– Joe Rice & Jeanne Houston, Primary Optical Watt Radiometer (POWR)
– Colleen Jenkins, Mike Lin, Technical Support
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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Things Dave Harber has been up to at LASP with
SIRCUS lasers and L-1 cryo radiometer
• Previously:
– Used the SIRCUS lasers to measure the flight TSIS SIM Fery prism
transmission from 211-2400 nm
• This is a measurement of the Fresnel reflection and Aluminum reflection
losses in the Fery prism
– Using the SIRCUS lasers and the Cryogenic Radiometer, we calibrated
the TSIS SIM electrical substitution radiometer (ESR) from 211 nm to
2400 nm
• Currently:
– Using the SIRCUS lasers to calibrate the wavelength scale of the SIM
flight instrument and to measure the instrument response function as
a function of wavelength and pointing, from 211 nm to 2400 nm
• Up Next:
– Use the SIRCUS lasers and the Cryogenic Radiometer to calibrate the
end-to-end radiometric sensitivity of SIM, from 211 nm to 2400 nm
Solar Spectral Irradiance (SSI) Variations Workshop
2012 February
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