LASP / University of Colorado

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Jerald Harder, Juan Fontenla, Byron Smiley, Sean Davis, George Lawrence and

1 The SORCE SIM Instrument: Progress Toward Spectral Irradiance Time Series Throughout the nm Region. Jerald Harder, Juan Fontenla, Byron Smiley, Sean Davis, George Lawrence and Gary Rottman LASP / University of Colorado Jerald.harder@lasp.colorado.edu 2003 SORCE Science Meeting Harder et al. -Page 1

2 Presentation Outline The SIM Instrument Review of instrument attributes Optical properties Electrical Substitution Radiometer (ESR) Resolving power Operational modes The Solar Spectrum and Solar Variability as Measured by SIM Comparison with other measurements over a limited wavelength range Examples of solar variability Current Instrument Issues, Conclusions and Outlook 2003 SORCE Science Meeting Harder et al. -Page 2

3 Optical Properties Overview Sun IR Vis2 Vis1 ESR 35 mm Fery Prism UV Focal Plane Optical Characteristics Value Resolution (nm) Resolving Power Spectrometer f/# Solar f/# f/16 f/115 Prism Aperture (mm) Effective Focal Length (mm) 400 Slit Sizes (mm) Scan Range in Focal Plane ±2.5º Optical Aberrations at Exit Slit (µm) 5 Diffraction Correction (%) mm From Entrance Slit To ESR Suprasil 300 R=435.3 mm Concave o R=445.4 mm Aluminized Convex 2003 SORCE Science Meeting Harder et al. -Page 3

4 Spectral Resolution 2003 SORCE Science Meeting Harder et al. -Page 4

5 ESR Detector Bolometer thermistors part of a precision AC bridge excited at 50 Hz Incoming solar beam chopped by shutter at 0.01 Hz and signal detected at shutter fundamental At 0.01 Hz & 200 sec integration period, noise=0.2 nw/ Hz 2003 SORCE Science Meeting Harder et al. -Page 5

6 SIM Normal Science Operation Modes Photodiode Fast Scan Gives orbit-to-orbit solar variability 6 samples per slit width Calibration tied to ESR values ESR Full Scan Measures the sun using phase sensitive detection method Very slow: requires 15 orbits to complete 3 samples per slit width ESR Table Scan IR Scan Table of 63 selected wavelengths that are tracked throughout the mission ESR in phase sensitive detection mode 2.6 samples per slit width (minimum spectral sampling) Fixed Wavelength Scan Engineering mode to study stability of the system 2003 SORCE Science Meeting Harder et al. -Page 6

7 SIM ESR Irradiance Spectrum June 4, 2003 ESR full scan requires 15 orbits to complete ESR response has very weak λ dependence 2003 SORCE Science Meeting Harder et al. -Page 7

SIM Brightness Temperature, March 4, 2003 T I b a hν = k 4 2hν 1 ln + 1 2 c λ I a = Solar Radiance -2 1 1 (Wm nm sr )

8 SIM Brightness Temperature, March 4, 2003 T I b a hν = k 4 2hν 1 ln c λ I a = Solar Radiance (Wm nm sr ) Removes Planck Blackbody contour from the spectrum Enhances spectral details 2003 SORCE Science Meeting Harder et al. -Page 8

9 Comparison Against Other Standard Works Fractional Difference From Average SIM (δ): δ = x SIM SIM SOLSPEC: Thuillier et al. Metrologia, 35, 689, 1998 {Composite 1} Davos: Wehrli, C., World Radiation Center (WRC) Publication No. 615, Davos-Dorf, Switzerland, July SORCE Science Meeting Harder et al. -Page 9

10 Comparison By Brightness Temperature 2003 SORCE Science Meeting Harder et al. -Page 10

11 PSPT Images 2003 SORCE Science Meeting Harder et al. -Page 11

12 Spectral Solar Variability Time Series 2003 SORCE Science Meeting Harder et al. -Page 12

13 Spectral Solar Variability Time Series 3 Months 2003 SORCE Science Meeting Harder et al. -Page 13

14 Current Instrument Issues: Analysis of photodiode detector stability is needed to improve the quality of the time series. All degradation processes must be studied and included in routine data processing Continue analysis of ESR efficiency need to complete calibration. Conclusions: SIM measurements cover the 200-~3000 nm region. Multiple detectors are required to meet the needs for solar spectral irradiance. Current method of treating prism degradation is effective Outlook: The combination of the SIM, TIM PSPT image analysis, and the RISE solar spectrum synthesis will provide a very valuable set of tools for studying solar variability SORCE Science Meeting Harder et al. -Page 14

Capabilities of NIST SIRCUS for Calibrations of SSI Vis-IR Instruments

Capabilities of NIST SIRCUS for Calibrations of SSI Vis-IR Instruments Steve Brown National Institute of Standards & Technology Gaithersburg, MD steve.brown@nist.gov; 301.975.5167 Answer: Ask LASP folks