This README file describes the format of the regular (non-profile) 6-channel Ames Airborne Tracking Sunphotometer (AATS-6) results 
obtained during ACE-Asia aboard the NCAR C-130.

The file names show the UT date on which most of the data in any given file was taken. However, the UT time in the 
first column starts with 00:00:00 on the date that is given in the second line of the file header. For example in file 
RF01_A6_31Mar01_all_r.asc the file date (see line 2 of file header) reads 3/30/2001 and the UT time in the first line starts 
at 23.78. Hence, do not extract the UT date from the file name but from line 2 of the file header.


The data are Q/A-ed and obstructions by clouds or aircraft structures have been removed. The current version (4.0) uses the 
RAF-distributed reference altitudes. For comparison with other investigators' data we recommend that their data be projected 
on the RAF reference altitudes as well. The curent version of AATS-6 data is also corrected for diffuse light entering AATS-6's 
field of view. For an explanation of these corrections, please see the statement posted at 
http://geo.arc.nasa.gov/sgg/ACE-Asia/Data_Plots/diffuse.html. 


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. 


We have computed fit coefficients for AOD that will allow you to interpolate the values to any desired wavelength in the range 
from 380 to 1021nm using a simple Angstrom law.


The fit is 



ln (tau_aero) = a0_Angstrom - alpha_Angstrom * ln (lambda) 

(the minus sign here differs from the profile files).



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


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



Note that:



AOD(4) expands to 4 variables (corresponding to the 4 wavelengths given in the header) 
AOD_Error(4) expands to 4 variables  (corresponding to the 4 wavelengths given in the header)




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:



Jens Redemann/Beat Schmid/Phil Russell/John Livingston
NASA Ames Research Center
MS 245-5
Moffett Field, CA 94035-1000
jredemann@mail.arc.nasa.go