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Trace gas and AOD retrievals from a newly deployed hyper-spectral
airborne sun/sky photometer (4STAR)
M. Segal-Rosenheimer, C.J. Flynn, J. Redemann, B. Schmid, Y. Shinozuka ,S. Dunagan, R.R. Johnson, J.M. Livingston,
P.B. Russell
• 4STAR (Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research) is a collaborative development by NASA Ames, PNNL, and NASA Goddard
• Instrument Features– AATS-like sun tracking
• Aerosol Optical Depth (AOD) at 13 wavelengths• H2O vapor column• Airborne - Horizontally and vertically resolved
– AERONET-like direct beam+ sky scanning• AOD• Size distributions (mode-resolved)• Single-scattering albedo (SSA)• Asymmetry parameter • Sphericity
– Hyperspectrally resolved (>1,000 channels) • Two spectrometers (UV-Vis-NIR and SWIR)
4STAR - Introduction
4STAR Head on DOE G-1
Figure: Internal scheme of the instrument.
Fiber optic & electrical cable to spectrometers & controls in cabin
• Direct Sun Mode – AOD/Trace gases
• Direct Sun Mode – Cirrus Optical Depth/Deff
(Segal-Rosenheimer et al., in preparation)
• Sky Radiance Mode – Size Distributions, SSA (Kassianov et al. submitted)
• Zenith Mode – Cloud Optical Depth (w upwelling flux)
4STAR – Data Products
4STAR – Data Products
• Direct Sun Mode – AOD/Trace gases
• Direct Sun Mode – Cirrus Optical Depth/Deff
(Segal-Rosenheimer et al., in preparation)
• Sky Radiance Mode – Size Distributions, SSA (Kassianov et al. submitted)
• Zenith Mode – Cloud Optical Depth (w upwelling flux)
Gas Retrievals
Water Vapor (H2O)Instrument Calibrated TOA spectrum
(SCHMID ET AL. 1996)
𝑇𝑤=𝑒𝑥𝑝 [−𝑎 (𝑚𝑤𝐶𝑊𝑉 )𝑏 ]
𝐶𝑊𝑉= 1𝑚𝑤
[ 𝑙𝑛 (𝑇𝑤 )−𝑎 ]
1𝑏
𝑇𝑤=𝐶𝑜𝑢𝑛𝑡 ( 𝜆 )𝐶0𝑚𝑜𝑑
𝐹𝑒𝑥𝑝(∑
𝑖=1
𝑛
𝜏 𝑖𝑚𝑖)
Gas Retrievals
Classic Direct Sun DOAS Method (e.g. Herman et al., 2009)
MLR (Multiple Linear Regression)
Relative spectrum TOA Langley spectrum
Spectral range (400-440 nm) Spectral range (440-625 nm)
High Order Polynomial (Rayleigh and Aerosols) Accurate Rayleigh Subtraction (Fit Aerosols with 2nd order Polynomial)
Shift and Stretch fit during retrieval Shift and Stretch fit before retrieval
Non-Linear Least Squares Linear Least Squares
Retrieved gases: Retrieved gases:
NO2, O3, O2-O2, H2O H2O from 940 regionNO2, O3, O2-O2
NO2/O3
Swap-in new spectrometer just before the campaign – still not well characterized!
ResultsTCAP (Two Column Aerosol Project Campaign)
• Airborne (DOE G-1, NASA LaRC King Air)• Surface (DOE AMF-1, MAOS)• July 7-29, 2012• Cape Cod, MA
AMF Ground SiteTwo column location
Hyannis Airport
Sample spectra (July 21st 2012)
Residual
Weak water vapor lines
Better characterization of spectrometer FWHM is still needed (not constant).
G-1 track and OMI overpass (July 22nd)NO2 levels
RMS difference= 4x1015 [molec cm-2] = 0.15 DU
OMI Overpass : 17:03 UT
Summary and Future Work
Preliminary science products:H2O, O3, NO2
AOD
Gas retrievals should and can be improved by:Better instrument slit function characterizationCombination of lamp and Langley calibration
Additional validation and comparison work is planned:DOAS group (Ground ARM site) – NO2 profilesBetter characterization of ozone profile, H2O from radiosonds
4STAR showed full operational capability in its first science campaign:Sun trackingBoth spectrometers (UV-Vis-NIR + SWIR) collecting data
Zenith viewing Sky Scanning