How to manually set an Ozone content in FLAASH

The following information describes how a user can manually set an ozone content prior to running FLAASH.

In order to hardwire a new, constant ozone value for all MODTRAN runs, open the tape5_1, the root tape5 file, in C:\Program Files\RSI\IDL63\products\ENVI43\bin\flaash\ACC\Workingdir\tape5_1. The ozone value is on card 1A, the second line in the file:
F 8F 0 355.00000 0.00010 0.000 F T F

The ozone data is in columns 31-40. Here the value is ' 0.000'. MODTRAN reads it initially as a string, and the zero value means "default to standard ozone column for the atmosphere selected". Other possibilities are summarized by the relevant section from the MODTRAN user manual [MODTRAN4 Version 2 USER’S MANUAL, A. Berk et al., 1 June 1999 (Last Revised 17 April 2000)]:

O3STR Vertical ozone column character string. If blank or 0., the default ozone column is used. If the first non-blank character is 'g', the ozone column in gm / cm2 follows 'g' (e.g., g 0.0001). If the first non-blank character is an 'a' the ozone column in ATM-cm follows 'a' (e.g., a 0.2). Otherwise, a positive value is interpreted as a scaling factor for the ozone column (e.g. 2.0 doubles the default ozone column). One Dobson unit equals 10-3 ATM-cm at 273.15 K. O3STR should not be used with a constant pressure path, i.e., MODEL = 0 on CARD 1.

We suggest using the multiplier method, but the other two are also possible. FLAASH defines this quantity as a string (o3col), and simply passes it through to the output tape5's. However, the ozone absorption in the 0.4-2.5 micron range of most sensors is small in vertical paths to space (a couple of percent or so in the Chappuis band), so the effect of likely variations from the default should be hard to discern.

Review on 12/31/2013 MM