The empirical transmission functions for molecular absorption in the widely used computer code called Lowtran are analyzed from a computerized numerical approach. Continuous functions are first adapted to the empirical functions, and then the absorber and spectral parameters are determined simultaneously for transmittance data in the major absorption bands of H(2)O, O(3), and the uniformly mixed gases. The analysis indicates that the transmission function parameters for Lowtran may be easily, and accurately, redetermined using numerical methods. This opens the possibility for code extensions to other absorbers, frequencies, spectral resolutions, absorber concentrations, as well as to recent transmittance measurements on the major absorbers.