4 STAR Spectrometer for SkyScanning SunTracking Atmospheric Research

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

4 STAR: Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research AERONET-like • Phase function • Size mode distributions • nre(l), nim(l) • Single-scattering albedo • Asymmetry parameter • Shape • Hence aerosol type Improve H 2 O, O 3 Add NO 2 Thus improve AOD Simultaneous spectra yield airborne profiles of aerosol type via Aeronet-like retrievals AATS-14 - like column and profiles • Aerosol • H 2 O • O 3

4 STAR and its Use

AATS-14 NASA Ames Airborne Tracking Sunphotometers Since 1996 • 13 Field Campaigns • >70 Publications AATS-6

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

Key Technological Hurdles 1. Maintaining calibration to 1% over a period of months 2. Stray light rejection: measure skylight within 3° of sun 3. Fiber optic couplings with <1% calibration stability (Connections/Rotation) 4. Sky scan within 100 seconds(10 km in flight)

Ground Prototype (4 STAR-Ground) ` Zeiss MCS CCD spectrometer Quasi-monolithic, no moving parts, ceramic body, Range: 250 -1016 nm, Resolution ~ 2 nm

Direct Beam Comparison AATS-14 4 STAR-Ground

Direct Beam Comparison AATS-14 & 4 STAR-Ground Transmittance UT

4 STAR-Ground AERONET Cimel Jens Redemann Roy Johnson

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

4 STAR and AERONET principal plane scan

Straylight rejection close to Sun

Size Distribution Retrieval using AERONET Code

Rotating Fiber Optics Coupling Throughput Repeatability

Next steps… • New collector design, 100 X light volume. Goal: Sky-scan measurements within 100 seconds, 10 km in flight • Mauna Loa, spectral Langley calibration • Add SWIR spectrometer for more size and absorption information • Continue spectral inversion development • Harden design for airborne deployment • Deploy in 2011: Western Atlantic Tropospheric Aerosol Campaign (WATAC)