[23] The 1800s saw
spectroscopic studies of the Sun advance, and Joseph von Fraunhofer made the first observations of
absorption lines in the spectrum, the strongest of which are still often referred to as Fraunhofer
lines.
The basic ingredients are easy to list: —
absorption / emission properties (or
spectroscopic parameters) of CO2 at atmospheric pressures, i.e. data presently available from HITRAN - database combined with models of
line broadening — observed properties of the atmosphere where most important features include clouds and moisture content, but many other factors have some influence — computer model of the transmission of radiation along the
lines of MODTRAN or GENLN2