Line parameter variations and the profile dependence of atmospheric transmittance.

Errors introduced by line parameter variations into atmospheric transmittance calculations in which the absorption line shape is assumed to be described accurately by the Galatry profile are compared with errors introduced by the use of approximate line profiles. Variations in two line parameters, the collision-broadened halfwidth at half-maximum (HWHM) under standard conditions, and the temperature dependence of the collision cross section are found to be significant. Calculations are presented that illustrate conditions for which variations in these two parameters will mask the profile dependence in a given transmittance calculation.