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)

Analysis MethodsAirborne Langley Calibration

Langley Flight: July 22nd - Off-coast Cape-Cod

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

𝐹 𝑒𝑥𝑝(∑𝑖=1𝑛

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

Water Vapor (H2O)Flight: July 21st - Off-coast Cape-Cod

Relative SD = 2%

Sample spectra (July 21st 2012)

Residual

Weak water vapor lines

Better characterization of spectrometer FWHM is still needed (not constant).

July 21st G-1 Flight path

Hyannis Airport

AMF Ground Site

Ocean spirals

[UT Time]

G-1 track and OMI overpass (July 21st)Ozone levels

RMS difference = 33 [DU]

OMI Overpass : 16:20 UT

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: O3/NO2

Sample AOD values (July 15th and 21st)

Scattered clouds

Summary and Future Work

Preliminary science products:H2O, O3, NO2

AODGas 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

THANK YOU!

Major funding from:

- NASA Radiation Science Program- Battelle PNW Division

- Department of Energy and ARM- NASA Post-Doctoral Program- Weizmann Institute of Science