Simultaneous measurements of water vapor and methane in the atmosphere were performed. Comparative measurements have shown that the modifications of the spectroscopic method and instrumentation used in water vapor and methane contents measurements in the atmosphere may be effectively used for long term monitoring of the gases and their variability. The improvement of accuracy in water vapor and methane contents measurements in the atmosphere is connected with the advancement of the techniques and the use of atmospheric models maximally approximated for the conditions of measurements and of a more completed comprehensive information on parameters of fine spectra of atmospheric gases for interpretation of recorded solar radiation absorption spectra.