*SEC Section

RFM Driver Table Sections: Ray Path
15APR25
Type
Primary Section#6
Alternative name for *TAN section when ray-path is specified by sec(zenith angle), equivalent to 'air mass factor', (ZEN or NAD flags)

Description
Define secant[1] of ray-path

Format
Multiple fields, any order
Field Type Description Units Range
SECFIL C200 Name of a Data File [2]
SEC R sec(zenith angle)[1] ≥1
Type: R=Real; Cn=character string, length n.

Notes
  1. SEC: Zenith angle is the angle from the vertical, so sec(zen.ang)=1 for a vertical path, and for slant paths the secant represents the 'air mass factor'. The same (+ve) definition is used for both ZEN and NAD directions, although it might be argued that SEC values should be negative for downward-viewing.

  2. SECFIL The type of field is identified by first using the Fortran INQUIRE statement to see if it is a file (assumed to be a .dat file), in which case the file is opened and the numbers read from the file as if they were directly inserted within the section at that point. This can be used in combination with actual numerical fields.

Examples
Downward-viewing calculations for plane-parallel atmosphere (NAD Flag).
*SEC 1.0 2.0 ! Vertical and 60deg views

Bugs
None recent