This README file describes the format of the 14-channel Ames Airborne Tracking 
Sunphotometer (AATS-14) results obtained during ACE-Asia aboard the CIRPAS
Twin Otter.

The data are Q/A-ed and obstructions by clouds or aircraft structures have been removed
or flagged. There are data that have AOD_flag=0 this means the AOD in one or more
channels are BAD but the water vapor is OK. Thus for AOD: only use data if AOD_flag=1. 


The filenaming convention is

CIRxx_A14_ddMonyy_all_r.asc

where xx=flightnumber, A14 (for AATS-14), date (on which file was started), "all" for data
of entire flight  and "r" for regular. 
Times can be larger than 24UTC if the file was started on the previous day. 

Versions are explained in revision.txt

We have computed fit coefficients for AOD that will allow you to interpolate the values to any 
desired wavelength in the range from 350 to 1560nm. 

The fit is 

ln (tau_aero)=a0 + a1 * ln (lambda) +a2 * (ln (lambda))^2 

where lambda has to be in units of micrometers. In the coefficient columns in the files the
first column is a2, the second is a1 and the third is a0. We highly recommend using this
interpolation in cases where the wavelengths don't match. 

We find that the AOD at 1060 nm are slightly high compared to 1020 nm despite the fact that 
we are applying a correction for 02-02 absorption. The 1060 nm wavelength should be used with 
caution. It is not used in the fit described above.


The exact format is described in the header of each file.

Note that in earlier versions:
AOD(13) expands to 13 variables (corresponding to the 13 wavelengths given in the header)
AOD_Error(13) expands to 13 variables  (corresponding to the 13 wavelengths given in the header)
fit_coeff expands to 3  variables  (as described above)

The files are pretty much self explanatory. But please do not hesitate to e-mail us for questions.


The retrieval algorithms are described in:

Russell, P. B., J. M. Livingston, E. G. Dutton, R. F. Puschel, J. A. Reagan,
T. E. Defoor, M. A. Box, D. Allen, P. Pilewski, B. M. Herman, S. A. Kinne, and 
D. J. Hofmann, 1993: "Pinatubo and Pre-Pinatubo Optical-Depth Spectra: Mauna Loa
Measurements, Comparisons, Inferred Particle Size Distributions, Radiative Effects,
and Relationsship to Lidar Data". Journal of Geophysical Research, Vol. 98, No. D12,
22'969-22'985.

Schmid B., C. Mätzler, A. Heimo, and N. Kämpfer, 1997: Retrieval of Optical Depth
and Size Distribution of Tropospheric and Stratospheric Aerosols by Means of Sun 
Photometry. IEEE Transactions on Geoscience and Remote Sensing, Vol 35, No. 1, 172-182.

Schmid, B., J. M. Livingston, P. B. Russell, P. A. Durkee, H. H. Jonsson, D. R. Collins,
R. C. Flagan, J. H. Seinfeld, S. Gassó, D. A. Hegg, E. Öström, K. J. Noone, E. J. Welton,
K. J. Voss, H. R. Gordon, P. Formenti, and M. O. Andreae, Clear sky closure studies of
lower tropospheric aerosol and water vapor during ACE 2 using airborne sunphotometer,
airborne in-situ, space-borne, and ground-based measurements, Tellus, B 52, 568-593, 2000.

Schmid B., J.J. Michalsky, D.W. Slater, J.C. Barnard, R.N. Halthore, J.C. Liljegren,
B.N. Holben, T.F. Eck, J.M. Livingston, P.B. Russell, T. Ingold, and I. Slutsker.
Comparison of columnar water-vapor measurements from solar transmittance methods.
Applied Optics, Vol. 40, No. 12, 1886-1896 (2001).



Point of contact:

Beat Schmid/Jens Redemann/Phil Russell/John Livingston
NASA Ames Research Center
MS 245-5
Moffett Field, CA 94035-1000

Phone: +1 650 604 5933
Fax:   +1 650 604 3625
e-mail: bschmid@mail.arc.nasa.gov

Check out our Web site http://geo.arc.nasa.gov/sgg/AATS-website/ for regularly for updates.