1. 1 SI Traceability for Climate Measurements Gerald Fraser, Carol Johnson, and Raju Datla, Joe Rice, Eric Shirley Optical Technology Division National Institute of Standards and Technology gerald.fraser@nist.gov

2. TOPICS OF INTEREST Traceability + Traceability on Orbit NIST Facilities - Scale realization/transfer strategy What do YOU think?

3. 3 Reflected Solar IR Thermal Emission Measurement of Optical Radiation & Climate R Earth Solar Constant ~ 1366 W m -2 ~0.30

5. 5 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)

6. 6 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

7. 7 Quality of Traceability Claim Quality 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

8. 8 … 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

9. NIST facilities/capabilities Presented: POWR Primary Optical Watt Radiometer SIRCUS Spectral Irradiance & Radiance Calibration using Uniform Sources AAMMAperture Area Measuring Machine HIPHyperspectral Imaging Projector Not presented: LBIRLow-Background Infrared Radiometry RSLRemote-Sensing Laboratory R2TRadiance & Radiance Temp., replacing FASCAL, FASCAL2, Heat Flux Facility STARRBRDF facility

10. 10 Jeanne Houston Joe 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)

11. 11 Tunable Laser Wavemeter Integrating Sphere Exit Port Spectrum Analyser Lens Detector Under Test Computer Reference Detector Intensity Stabilizer Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) Monitor Detector (output to stabilizer) =UV to LWIR Chopper or Shutter Speckle- removal System with the aid of SIRCUS Keith Lykke Steve Brown George Eppeldauer

12. 12 …and to the Meter through Aperture Area Measurements Performed by the Absolute Aperture Area Measurement Machine… Aperture area to better than 0.01% Toni Litorja Joel Fowler

13. Detector-based temperature realization in SIRCUS Realization, dissemination of temperature scales above Ag freezing point

14. Scene viewed by a typical optical sensor instrument Scene viewed by an Imaging instrument In practice Consider the complexity of real-world scenes: Hyperspectral Imaging Projector (HIP)

15. 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.

16. Digital Light Processing (DLP) Projectors Reference: www.dlp.comwww.dlp.com

17. Hyperspectral Image Projector (HIP) Prototype L6 DMD1 Illumination Optics Homogenizer Projection Screen Fold Mirror Projection Optics DMD2 Beam Stop 2 Spatial Engine Unit Under Test (UUT) (or Reference Instrument) Spectral Engine Band M Spectral Image Band M Spatial Image Beam Stop 1 L3 M1   Prism2 Prism1 L4 L2 L1 Supercontinuum Fiber Laser L5 Can substitute with other foreoptics to present to UUT

18. How the DMD is used to create an arbitrarily programmable spectrum

19. 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)

20. Example image as projected by the prototype HIP onto a white screen and taken using a digital camera

21. 21 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)

22. EXTRA SLIDES FOLLOW

23. 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. Supercontinuum Fiber Laser: A “White” Broadband Laser

24. Comparison of Matched Spectra: Xe Lamp vs Supercontinuum With Xe Lamp, Vegetation Spectrum Spectral Images (on DMD) With Supercontinuum Fiber Laser

25. 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 Endmember Spectra EM-2 EM-3 EM-5 EM-4 EM-6 EM-7 Then we need only project N = 6 broadband spectra instead of M = 30+ monochromatic spectra. Endmember decomposition