The variable H2O overwrites the predefined H2O total column concentration from the selected atmospheric model in MODEL by the user input H2O value in [g·cm-2]. Typical worldwide and annual H2O concentrations range from 1 g·cm-2 to 6 g·cm-2, with typical mean values around 3 g·cm-2. Note that libRadtran requires units of mm (10 mm=1 g·cm-2). ALG does this unit conversion automatically.
Atmospheric transmission curve calculated using MODTRAN v4.2
for a 1976 US Standard atmosphere.