Part 1: New spectral stuff going on at NIST. Part 2: TSI Traceability of TRF to NIST

Transcription

1 Part 1: New spectral stuff going on at NIST SIRCUS-type stuff (tunable lasers) now migrating to LASP Absolute Spectrally-Tunable Detector-Based Source Spectrally-programmable source calibrated via NIST detector Could replace some lamp-illuminated integrating sphere apps Research at NIST in progress to demonstrate stability and accuracy Hyperspectral Image Projector (HIP) A dispersed supercontinuum white-light laser source is used to simulate spectra at 2 nm resolution. Part 2: TSI Traceability of TRF to NIST Optical Technology Division TSI TRF Calibration against NIST POWR Page 1

2 Absolute Spectrally-Tunable Detector-Based Source Broadband vs Narrowband Operation Steve Brown et al., NIST For more details, see Brown et al., Proc. SPIE 7807, 78070A (2010) Optical Technology Division TSI TRF Calibration against NIST POWR Page 2 2

3 Spectral Radiance (W/m 2 sr um) Spectral Radiance (W/m 2 sr um) HIP simulating Top-of-Atmosphere (TOA) Solar Spectrum Joe Rice, paper in progress Left panel shows the maximum HIP radiance and reflected solar radiance Right panel is an expanded scale: Red shows HIP output matched OLI Matching Absolute_Maximum OLI Matching Absolute Measured to some from HIP typical Prototype VNIR Earth-reflected Spectral Engine 11/3/10 spectra in the Visible-Near IR (VNIR) Measured from HIP Prototype VNIR Spectral Engine 11/3/10 Modeled Spatial Engine: XGA DMD f/3 with 20% Transmittance Modeled Spatial Engine: XGA DMD f/3 with 20% Transmittance HIP VNIR Limits 6000 HIP VNIR Limits TOA Solar Bare Desert Soil 1000 TOA Solar 100 Vegetation Wavelength (nm) Wavelength (nm) Optical Technology Division TSI TRF Calibration against NIST POWR Page 3

4 Comparison of the Total Solar Irradiance Radiometer Facility Cryogenic Radiometer against the NIST Primary Optical Watt Radiometer Joseph P. Rice and Allan W. Smith Optical Technology Division National Institute of Standards and Technology (NIST) Gaithersburg, Maryland Greg A. Kopp, David M. Harber, and Karl F. Heuerman Laboratory for Atmospheric and Space Physics (LASP) University of Colorado Boulder, Colorado Steven R. Lorentz L-1 Standards and Technology New Windsor, Maryland Contact: Optical Technology Division TSI TRF Calibration against NIST POWR Page 4

5 Cryogenic Electrical Substitution Radiometry Thermalized optical laser power is compared to thermalized electrical power in a black cavity Generally, active cavity radiometers in vacuum at 2 K to 5 K Primary standard at NIST and in most other industrialized nations for optical power responsivity of transfer detectors such as Si-diode trap detectors Intercompared internationally via portable transfer detectors at 0.02% (k=2) uncertainty Liquid Nitrogen Liquid He at 2K Primary Optical Watt Radiometer (POWR) Optical Technology Division TSI TRF Calibration against NIST POWR Page 5

6 International Intercomparison of Cryogenic Radiometers Standards labs can measure responsivity of traps to <1 mw laser power to about 0.02% This was in the late 1990 s, and NIST numbers are from HACR (predecessor to POWR). BIPM report: Optical Technology Division TSI TRF Calibration against NIST POWR Page 6

7 10 4 x Difference from the Mean Intercomparison of Present-Day Standard NIST Cryogenic Radiometers POWR 27Apr05 Intercomparis nm 514 nm 633 nm L-1 POWR LOCR Optical Technology Division TSI TRF Calibration against NIST POWR Page 7

8 Introduction to the Intercomparison Reported in This Talk LASP has now developed a facility for pre-flight calibration of TSI Instruments Total Solar Irradiance (TSI) Radiometer Facility (TRF) System-level calibration in irradiance mode at TSI irradiance level (68 mw for TIM) This is the first ever facility capable of this feat at less than 0.1% uncertainty level Motivated by the need for improved TSI measurement accuracy Supported by the NASA Glory Project Used for Glory Total Irradiance Monitor (TIM) The irradiance scale is based upon a new cryogenic radiometer: TRF Radiometer Cryogenic radiometers are in use worldwide and yield the lowest uncertainty Typical uncertainty of order 0.01% (k=1) (=100 ppm), but only at 2 mw power level The TRF Radiometer is optimized for 68 mw power level: first of its kind What is the radiant power scale uncertainty of the TRF Radiometer? 1. Can be determined from the components, as for any active cavity radiometer AND/OR 2. Can be assigned based in large part upon transfer from a NIST cryogenic radiometer, such as the NIST Primary Optical Watt Radiometer (POWR) This talk describes a scale comparison of the TRF Radiometer with the NIST POWR Result: NIST Correction of TRF native scale by +306 ppm with an uncertainty of 98 ppm (k=1) is required to calibrate it on the NIST POWR scale Optical Technology Division TSI TRF Calibration against NIST POWR Page 8

9 Beam From 532 nm Laser Experiment Description Part 1 Align translation stage so that laser beam enters POWR. Adjust ½ wave plate to turn power to 2 mw. Record POWR shuttered power measurements and both Si trap photodiode signals. Beamsplitter 2 Trap Photodiode 2 POWR Brewster Window ½ Wave Plate Shutters Trap Photodiode 1 POWR 2 mw Intensity Stabilizer Spatial Filter Polarizer Beamsplitter 1 TRF Radiometer Brewster Window Translation TRF Stage Radiometer Optical Technology Division TSI TRF Calibration against NIST POWR Page 9

10 Beam From 532 nm Laser Experiment Description Part 2 Move translation stage so that laser beam enters TRF Radiometer. Adjust ½ wave plate to turn power up to 68 mw. Record TRF Radiometer shuttered power measurements and both Si trap photodiode signals. Beamsplitter 2 Trap Photodiode 2 POWR Brewster Window POWR ½ Wave Plate Shutters Trap Photodiode 1 68 mw Translation Stage Intensity Stabilizer Spatial Filter Polarizer Beamsplitter 1 TRF Radiometer Brewster Window TRF Radiometer Optical Technology Division TSI TRF Calibration against NIST POWR Page 10

11 Servo Error (counts) Power (mw) Trap Response (V) Typical Raw Data SciData_REC TRF Shutter Cycles TRF Radiometer 0 TS TRF Shutter Cycle Trap Response Trap 1 Trap Photodiode Signals Heater Power Servo Error Time (s) Trap Time (s) Optical Technology Division TSI TRF Calibration against NIST POWR Page 11

12 Results Shuttered Laser Power Entering TRF Aperture Based only on POWR (i.e. what TRF should measure) P L NP r r P Corrections Trap Photodiode Responsivity (1) Rt Vt ' Trap Photodiode Response (2) Value Uncertainty Value Uncertainty Corrections (June 12, 2008) Component (June 13, 2008) Component R t V t ' mw 43 ppm mw 58 ppm Relative Window Transmittance r ppm ppm Relative Scatter r ppm ppm POWR Nonequivalence N ppm ppm POWR Absorptance ppm ppm POWR Electrical Scale ppm ppm POWR Corrected Value P L mw 90 ppm mw 97 ppm TRF Radiometer Value P TDVM mw 34 ppm mw 23 ppm P L / P TDVM ppm ppm P L / P TDVM Recommended Value Combined Uncertainty (k=1) 98 ppm Optical Technology Division TSI TRF Calibration against NIST POWR Page 12

13 Summary A scale comparison of the NIST POWR and the TRF Radiometer was performed 532 nm Radiant power (underfilled apertures), as opposed to irradiance mode (overfilled apertures) POWR at 2 mw, TRF Radiometer at 68 mw, two trap photodiodes used as transfer The TRF Radiometer shuttered power measurement reads low by the following amount: 306 ppm +/- 98 ppm (k=1) The TRF Radiometer native scale used here had not been explicitly corrected for its nonequivalence, cavity reflectance (about 38 ppm), or electrical power scale calibration Applying the recommended correction above intrinsically corrects for these effects A detailed report on this comparison is being written for a published journal article We thank the NASA Glory Project for supporting this work. Optical Technology Division TSI TRF Calibration against NIST POWR Page 13

14 Motivation: Laboratory sources do not simulate reality Optical imaging and spectral sensors are tested and calibrated with uniform/simple laboratory sources Examples: Lamp-illuminated integrating sphere Blackbody Standard bar or resolution charts But reality is spatially and radiometrically non-uniform and complex Example: AVIRIS image of North Island Naval Air Station, San Diego, CA Optical Technology Division TSI TRF Calibration against NIST POWR Page 14

15 Existing Spectral Radiance Scales Are Based on Lamps Spectroradiometers have not demonstrated the capability that they can maintain a scale at the 0.1% level (yet). Only about 1% (1sigma) at best. Typical results from spectroradiometer measuring lamp-illuminated sphere: Graphic courtesy of NIST s Remote Sensing Laboratory However, unfiltered radiance detectors have demonstrated the potential to hold a radiometric scale at the 0.1% level and better. Optical Technology Division TSI TRF Calibration against NIST POWR Page 15

16 Absolute Spectrally-Tunable Detector-Based Source Absolute detector measures radiance of single-line spectra These data are then used to set the spectral radiance scale use to calibrate spectroradiometer Spectrally-Tunable Source Absolute Radiance Detector Integrating Sphere currently lamp-based could be SC-based Apertures Si detector Control Computer Spectroradiometer Logging DVMs Spectroradiometer Input For more details, see Brown et al., Proc. SPIE 7807, 78070A (2010) Optical Technology Division TSI TRF Calibration against NIST POWR Page 16

17 Reflectance (ppm) Pressure (Torr) Reflectance (ppm) Stress-Induced Birefringence Changes Window Reflectance This common effect, though small with the 6 mm thick POWR window, was significant with the 3 mm thick TRF Radiometer window, and was corrected for both. POWR Window Reflectance: POWR Window Reflectance vs Time Venting from vacuum to atmosphere TRF Radiometer TRF Reflectance Window Vaccum-Air Reflectance: Cycles Alternating between vacuum and atmosphere Reflectance Pressure Cycle 1 Cycle 2 Cycle 3 Vacuum Closed Gate Valve Tweaked Window Alignment Here Atmosphere Time (s) Set Number Optical Technology Division TSI TRF Calibration against NIST POWR Page 17

18 Transmittance Transmittance Window Transmittance Scans in Air Relative window transmittance at 0 mm position was corrected. POWR Window POWR Window Transmittance Scans TRF Radiometer Window TRF Window Transmittance Scans Scan 1 Scan 2 Scan Scan 1 Scan 2 Scan Position (mm) Position (mm) Optical Technology Division TSI TRF Calibration against NIST POWR Page 18