2. Sergey Mekhontsev National Institute of Standards and Technology Optical Technology Division, Gaithersburg, MD 20899 Infrared Spectral Radiance Scale Realization and Transfer “NIST IR Radiometry for Climate Benchmark Traceability” Meeting Gaithersburg, MD, June 12, 2008

3. Outline Spectral Radiance: Definition and Significance Spectral Radiance Scale Realization Principles IR Spectral Radiance Scale at the AIRI Facility CBS3 Facility and CLARREO mission support

4. Definition: Radiant flux [  ] per unit projected area [A], per unit spectral interval, and per unit solid angle [  ] incident on, passing through, or emerging in a specified direction from a point in a specified surface Symbol: L(  Unit:W/(cm 3 ·sr) L Spectral Radiance - Definition A  Radiance is an invariant property of any lossless optical system. Typically, if radiometric device contains a pair of apertures separated by some distance, and both apertures are filled by the source, it measures radiance.

5. Detector Based IR Radiance Scale Realization 1. Can be used to measure BB temperature assuming it has unity emissivity, using Stefan-Boltzmann law (2) or (3) can be used with element-level calibration or together with (1) and tunable monochromatic sources 2. Can be used to measure radiance of a monochromatic source (could be explored)

6. Source Based IR Radiance Scale Realization

7. AIRI - National Primary Standard of IR Spectral Radiance Recently established Advanced Infrared Radiometry and Imaging (AIRI) Laboratory, among other functions, is enabling a national level traceability for measurements of absolute spectral radiance and spectral emissivity of BB sources and targets at near ambient temperatures at ambient environment. Fixed Point BB Bench Variable Temperature/Spectral BenchScene plate/Scatter Tool

9. Tunable Filter Comparator TFC TFC has capacity to consistently measure temperature with standard deviation from 5 to 25 mK in the range -50 °C to 250 °C across spectral regions to 3-5 and 8-12.5 micron Spectral Resolution Spatial Scatter Measured spectra Known Spectral Radiances of Ambient and Variable Temperature Reference BB’s

10. FTIR-Based IR Spectral Radiance Comparator Uncertainty Evaluation at 10 °C using FT Spectrometer Random Uncertainty of Comparison, Radiance Random Uncertainty of Comparison, Temperature -FT capability realized both at NIST and NPSL (Navy Primary Standards Lab) -Shown results are obtained at NPSL setup with SR-80 blackbodies at 10 °C

11. Water Bath BB Characterization °° - Current serve as Primary Standard at the Temperature Range 10 °C to 75 °C - Availability of two WBBB is instrumental for system uncertainty evaluation - So far performance is still comparator-limited

12. Ammonia Heat Pipe BB Characterization Refrigerated Bath, -65 °to +55 °C Refrigerated Bath, -65 °C to +55 ° C Cavity geometry Blackbody Design Gas heat Exchanger

13. Large Aperture Ga Fixed Point BB Ga FP BB (29.765 °C) is an important tool for further reduction of the uncertainty of near-ambient BB measurements. It is also expected to become a prototype for large aperture vacuum-compatible water (0.01 °C) and Mercury (-38.834 ° C) FP blackbodies

14. Thermal IR Scales – Internal Validation

15. Thermal IR Scales – International Comparisons

16. AIRI Near Ambient Scale Realization - Summary A systematic realization of IR spectral radiance and radiance temperature scales has been performed. Implemented AIRI capabilities include: –characterization in absolute spectral radiance and radiance temperature across the spectral range 2.5 µm to 13.5 µm and temperature range - 50 °C to 150 °C with typical comparison uncertainty 25 to 50 mK (k=2); –characterization of spatial uniformity and stability; –background radiation correction and emissivity (reflectance) evaluation for flat plate calibrators. Internal and international comparisons are being conducted to validate the uncertainties

17. What AIRI Has to, but Cannot Do? -Measure outside atmospheric transmission windows -Calibrate targets at set points and radiation backgrounds below 18 °C -Calibrate thermal IR targets which are designed to operate in vacuum -Expand to far-IR spectral range

18. Simplified Conceptual Design

19. Proposed Solution Top View Some details of design of the proposed multipurpose controlled background vacuum emissometer

20. CBS3 Concept

21. Chamber Hardware Chamber Specifications: - 4’ x 4’ x 8’ box with two 4’ x 4’ doors - Modular temperature controlled shroud, 200 K to 350 K

22. Anticipated CBS-3 Role in CLARREO Traceability

23. Summary Proven technical solutions and experience with IR spectral radiance realization at the AIRI facility demonstrated feasibility of building an environment–controlled extension – CBS3 facility. Along with continued support to NIST TXR and existing NASA customers, CBS-3 will support spectrally resolved radiance temperature measurements for targets at 190 K to 520 K at backgrounds from 190 K to 320 K across spectral band from 2.5 µm to 100 µm. It is anticipated that after moderate modifications, existing primary BB sources will be shared between the AIRI and a new CBS3 facility. CBS-3 will also accommodate a novel variable angle emissometer / reflectometer for characterization of materials and coatings over the aforementioned spectral and temperature ranges. The intended range and uncertainties of the spectral radiance / radiance temperature and material characterization capabilities make CBS-3 facility a cornerstone of the NIST proposed strategy for establishing nationwide traceability of IR remote sensing measurements, including climate change studies such as proposed CLARREO mission.