CLARREO Meeting June 12, 2008 CLARREO Traceability Concept and Demonstration Study Results Leonard Hanssen National Institute of Standards and Technology Gaithersburg, MD 20899

Two Parts: I.CLARREO Traceability Concept II.CLARREO Support Demonstration Study

System-level calibration: testing all systematic sources of measurement uncertainty on-orbit *Slide from John Dykema, Harvard U. CLARREO Mission On-board Calibration & Monitoring Concept

Background – NIST Role Achieving proven accuracy and traceability of spaceborne measurements to fundamental and reproducible physical standards is a keystone of the CLARREO mission. Current concept of the CLARREO mission envisages use of original concept of on-board reference BB with built-in means of controlling stability of cavity emissivity and temperature sensors. It is important, though, that this concept and its implementation undergoes a rigorous testing and is made traceable to the international standards prior to launch. NIST has expertise and most of hardware necessary for participation in the pre-flight sample-, component- and system-level studies and calibration of IR sensors

NIST Support for CLARREO Traceability

Materials and Optical Components Characterization Blackbody Source Calibration and Modeling Complimentary Calibration Possibilities IR Spectrophotometry Simon Kaplan IR Spectroradiometry Source Based Scale IR Spectroradiometry Detector Based Scale Sergey MekhontsevRaju Datla emittance BRDF - scattering polarization dependence linearity radiance temperature cavity emissivity - Modeling predictions - Radiance measurement - Reflectance measurement emissivity monitoring method(s) LBIR - low background transfer IR spectroradiometer linearity HIB scene generator

Current NIST IR Radiance Scale Realization (AIRI Facility) Cavity Coating Measurements (DHR, BRDF) (CHILR, BRDF)

Outline I.CLARREO Traceability Concept II.CLARREO Support Demonstration Study 1.Study plan overview 2.Materials characterization 3.Monte Carlo BB modeling 4.Direct BB characterization 5.Emissivity monitoring evaluation

Demonstration of Pre-Flight Cavity Emissivity Measurement and On-Board Monitoring Techniques for CLARREO Blackbody Prototypes Participants: NIST, HU, SSEC. GOAL: demonstration of emissivity Measurements, Modeling and Monitoring techniques for different on-board BB prototypes. NEAR TERM GOALS: implement Measurement and Modeling in next 4 months; report at NEWRAD, complete Monitoring activity by end of year. PRODUCTS : –Pre-flight (absolute) emissivity techniques; LEVEL OF AGREEMENT –On-board (relative) emissivity monitoring; PERFORMANCE and RECOMMENDATIONS

Demonstration Study Elements DHR Spectral directional hemispherical reflectance at FTIS Facility -Near-normal - Reference Integrating Sphere -Variable angle - Center Mount Sphere BRDF Bi-directional reflectance distribution function -Laser-based system, 1.32 & 10.6 µm Monte Carlo Modeling of Blackbody Cavity -STEEP3, 3.5 -Use Z306 DHR now, BRDF later Cavity Emissivity using Sphere Reflectometer -Same lasers as for BRDF -UW, HU blackbodies Blackbody Spectral Emissivity using AIRI Facility - two methods -Using scene plate setup and -Using spectral radiance measurement setup

Near Normal Integrating Sphere Specifications  range: µm 6 inch diameter gold-electroplated plasma-sprayed metal coating MCT detector w/ concentrator optics baffling in sphere 8° incidence angle Capabilities Reflectance, Transmittance & Absorptance Temperatures °C absolute & relative, specular & difuse, R, T & A uncertainties (2  ):  specular: ≤ 0.3%  diffuse: %  larger for angle dependent structure can measure R of accessories samples can sort out scatter from total R & T

Z-306 Spectral Reflectance Results NIST produced Z-306 sample Absolute Reflectance measured on Reference sphere, relative on center-mount sphere No discernable difference between 8 and 16 deg. Harvard sample exhibited some differences, but not at 10.6 µm Angular Dependence

BRDF at 1.55 and 10.6 µm Both s and p polarized input curves shown; output is measured in total mode Scattering angle is Note specular component at 10.6 µm; diffuse light is also more concentrated

Monte Carlo Modeling: Optical Property Modeling for Z306 paint (in order of increase of complexity and physical plausibility 1 st stage. Uniform Specular-Diffuse Model (USD, implemented in STEEP3 v. 1.3, allows to compute full spectrum per one run) ρ = ρ d +ρ s ; ρ ≠ f(θ i ); ρ d /ρ ≠ f(λ); ρ d /ρ = f(θ i ) 2 nd stage. Generalized Specular-Diffuse Model (GSD, implemented in STEEP3.5v): ρ = dR d +(1-d)R s = ρ d +ρ s ; ρ d = f(λ); R s = f(λ,θ i ) R s can be expressed by Fresnel law, Shlick approximation, arbitrary function, or look- up table 3 rd stage. TETRA BRDF model for random rough surfaces (implemented in STEEP4TM and to be implemented in STEEP4, v. 1.2) – see our paper in International Journal of Thermophysics, 28, (2008)

AERI BB STEEP3.5 Modeling Results

Harvard BB STEEP3.5 Modeling Results

3D plots of TETRA-G BRDF in spherical coordinates for three incident angles; β=2, n λ =2.5, k λ =2.0, λ=10.6 μm. All BRDF maxima are normalized to unity.

Complete Hemispherical Laser-Based Reflectometer Designed for complete hemispherical reflectance measurement using 20 cm gold integrating sphere with 6 mm entrance aperture (1/2 angle = 1°) and 50 mm sample port Laser sources: 10.6 µm, 1.32 µm (3.39 µm, µm available, µm potential) Detectors: MCT, pyroelectric and InGaAs; array, quadrant detectors for beam alignment and profiling Motorized stages used to manipulate sphere and cavity Map spatial uniformity & angle dependence Can measure reflectance down to approx (equivalent to emissivity ) Reflectance expanded uncertainties previously estimated % for to range, black sample R= within.0002 of spectral DHR Top View of Setup w/HU BB Side View of Setup w/HU BB View of Setup w/AERI BB

Harvard U. Blackbody Reflectance Spatial Map BB aperture is 1.5 in., sphere port is 2 in, central region (±6 mm) is exact, outside requires correction Performance at 1.32 µm roughly order of magnitude better than at 10.6 µm 1.32 µm 10.6 µm

Harvard U. Sectional Blackbody Scans BB aperture is 1.5 in., sphere port is 2 in, central region (±6 mm) is exact, outside requires correction Performance at 1.32 µm roughly a factor of two better than at 10.6 µm 1.32 µm 10.6 µm

AERI Blackbody Reflectance Spatial Map BB aperture is 2.75 in., sphere port is 2 in, these data require estimated correction Performance at 1.32 µm only factor of 1.5 better than at 10.6 µm 1.32 µm 10.6 µm

SSEC AERI Blackbody Scans Measurements performed with different apertures on BB, and no aperture Standard BB aperture is 2.75 in., sphere port is 2 in, correction in reflectance required (x 1.9) Performance at 1.32 µm only slightly better than at 10.6 µm 1.32 µm 10.6 µm

AERI Blackbody Setup at AIRI Facility

AERI Radiance Temp vs. Background

AERI BB Measured Spectral Emissivity Using AIRI Scene Plate and CVF spectroradiometer

Monte Carlo Modeling Task: Hemisperical vs. Partial Reflectivity of a Cavity Detector’s FOV Laser’s Beam Implemented in STEEP3 v. 1.3 as “Skew-Conical Effective Emissivity” observation scheme. Small source/Small detector scheme. Not implemented in STEEP software. Additional programming efforts are necessary (Shadow rays method)

Demonstration Study Results Summary Nearly Completed set of Measurements and Modelling (Harvard BB spectral radiance measurements being performed) Analysis and comparison of results begun On-board monitoring techniques modelling requirements being determined, implementation TBD Results already of benefit to HU, UW, discussions yesterday Results to be presented at NEWRAD (Oct. 08)

Back-Up Slides

Demonstration Study: NIST Publication References IR MATERIALS EMISSIVITY: NIST program for the infrared emittance characterization of materials, L. Hanssen, S. Mekhontsev, S. Kaplan, in Proc. Intern. Thermal Conductivity Conf. (ITCC), Birmingham AL, 2007, accepted to the Intl. J. Thermophys. (2008) NIST infrared reflectometer – emissometer, L. Hanssen, S. Mekhontsev, V. Khromchenko, A. Prokhorov – submitted to NEWRAD 2008 BB EMISSIVITY MODELING: Radiative properties of blackbody calibration sources: recent advances in computer modeling, A. Prokhorov, S. Mekhontsev, L. Hanssen, Int. J. Thermophys., 28, 2128 – 2144, BB EMISSIVITY MEASUREMENT: Evaluation of blackbody cavity emissivity in the infrared using total integrated scatter measurements, L. Hanssen, S. Mekhontsev, J. Zeng, A. Prokhorov, Int. J. Thermophys., 29, 352 – 369, BB IR SPECTAL RADIANCE MEASUREMENT: NIST radiance temperature and infrared spectral radiance scales at near-ambient temperatures, S. Mekhontsev, V. Khromchenko, and L. Hanssen, accepted to the Intl. J. Thermophys. (2008) A tunable filter comparator for the spectral calibration of near-ambient temperature blackbodies, V. Khromchenko, S. Mekhontsev, L. Hanssen, Proc. SPIE, Vol. 6678, 66781E E10 (2007) 4.7  m Reference Pyrometer for the Temperature Range -50 C to 150 C, V. Khromchenko, S. Mekhontsev, L. Hanssen, submitted to NEWRAD 2008 CLARREO-RELATED Design and evaluation of large aperture Ga fixed point blackbody, V. Khromchenko, S. Mekhontsev, L. Hanssen, accepted to the Intl. J. Thermophys. (2008) Infrared Spectroradiometry for Climate Benchmark Traceability: Approach and Demonstration Study, S. Mekhontsev, L. Hanssen, J. Zeng, V. Khromchenko, A. Prokhorov, J. Dykema, F. Best, submitted to NEWRAD 2008

Variable Angle Incidence Center Mount Sphere

CHILR Setup Cavity Integrating sphere Detector Sample rotation & X-Y stage Sphere rotation & X-Y stage 1.32 µm 10.6 µm

Measurement Sequence for Cavity Reflectance Cavity Cavity aperture Standard Reference Detector (a)(b) (c)(d) Beam Dump

Background/Scatter Component Subtraction Example: Complete V-groove Cavity Aperture w/ Front Section Only 10.6 µm 1.32 µm Final Cavity Reflectance for Emissivity