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4STAR: Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research

The 4STAR spectrometer is designed to measure aerosol properties for atmospheric research, including direct and indirect aerosol forcing. It can provide data on aerosol size distributions, optical properties, scattering phase function, and more. This collaboration between PNNL, NASA Ames, and NASA GSFC aims to improve our understanding of climate change and radiative forcing.

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4STAR: Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research

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  1. 4STAR: Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research A collaboration involving: PNNL: C. Flynn, B. Schmid, E. Kassianov NASA Ames: S. Dunagan, R. Johnson, Y.Shinozuka, P. Russell, J. Redemann, J.Livingston NASA GSFC: AERONET Team

  2. Motivation for a Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) • Future change in Earth’s surface temperature is driven by radiative forcing and climate sensitivity. • Uncertainties in radiative forcing of climate are still dominated by uncertainties in forcing by aerosols, • Directly (scattering and absorption of solar radiation) • Indirectly (through the aerosols’ effect on clouds) • 4STAR can measure many of the quantities needed to determine direct and indirect aerosol forcing (unperturbed by sampling artifacts)

  3. AERONET-like capability • Ground-based direct beam + sky scanning yields column-integrated aerosol properties: • Size distributions • Single-scattering albedo • Asymmetry parameter • Sphericity 4STAR: Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research AATS-like capability: Airborne sun-tracking yields range-resolved properties from column-integrated quantities measured while profiling. 4STAR: Improve gases And thus AOD Airborne spectra yields profiles of aerosol type

  4. Anticipated 4STAR data products: • Solar Direct Beam • Atmospheric Transmittance • Aerosol Optical Depth and Ångstrom exponent • Aerosol Extinction (via aircraft vertical profiling) • Gases: H2O, O3, NO2, CO2 (column and in profile) • Angularly-resolved sky radiance inversions • Scattering phase function, asymmetry parameter • Aerosol size distributions, fine/coarse mode fraction • Aerosol sphericity • Aerosol absorption • Zenith radiance cloud retrievals • Cloudy/clear transition zone (Marshak, Chiu) • Cloud Optical Depth, Droplet effective Radius (with auxilliary measurements, Barker et al.) • Water vapor, liquid water, ice water fractionation (Daniels et al.)

  5. 4STAR and its Use…

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  7. Fiber Optics Cable Motor Feedback Devices Optical Entrance Elevation Motor Aircraft Skin Azimuth Motor Slip Ring Fiber Optics Rotating Joint Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR)

  8. Ground Prototypes (4STAR-G)

  9. Key Technological Hurdles: • Fiber optic couplings with <1% calibration stability (Connections/Rotation) • Irradiance calibration to 1% over a period of months. • Radiance calibration to a few percent. • Stray light rejection: measure skylight down to within 3° of sun • Sky scan within 100 seconds (10 km in flight) • Stray light inside spectrometers

  10. Rotating Fiber Optics CouplingThroughput Repeatability

  11. 4STAR-Ground AERONET Cimel NASA Ames 30” Sphere Radiance Calibration

  12. 4STAR-Ground AERONET Cimel Jens Redemann Roy Johnson

  13. Stray light rejection close to Sun - old barrel

  14. Size Distribution Retrieval using AERONET Code

  15. Sun Photometer Inter-Comparison Experiment Mauna Loa, Aug. 24-Sept. 2 2008 AATS-14 Prede 4STAR 3 Cimels

  16. Stray light inside Spectrometers 19

  17. Stray light inside Spectrometers 20

  18. Next steps… • Adding temperature-stabilized enclosure for data acquisition rack • Finish stray light in side spectrometer correction • Reduce stray light in skylight measurements • Build airborne version FY10 and FY11. • Modify G-1 escape hatch for integration of 4STAR in FY10 • Test-fly 4STAR on G-1 in FY11. • Hardening and retrieval algorithms in FY12 Funding: NASA, DOE ARM, BMI, PNNL

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