Sergey Mekhontsev National Institute of Standards and Technology

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

2. 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

3. Spectral Radiance - Definition w L 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.

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

5. Source Based IR Radiance Scale Realization

6. 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 Bench Scene plate/Scatter Tool

8. Tunable Filter Comparator TFC • Known Spectral Radiances of Ambient and Variable Temperature Reference BB’s • Measured spectra Spectral Resolution 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 Spatial Scatter

9. FTIR-Based IR Spectral Radiance ComparatorUncertainty Evaluation at 10 °C using FT Spectrometer 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 Random Uncertainty of Comparison, Radiance

10. 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

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

12. 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

13. Thermal IR Scales – Internal Validation

14. Thermal IR Scales – International Comparisons

15. 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

16. 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

17. Simplified Conceptual Design

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

19. CBS3 Concept

20. 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

21. Anticipated CBS-3 Role in CLARREO Traceability

22. 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.