The analysis of integral form of the radiative transfer equation shows that vertical gradients of temperature profiles in the atmosphere are the major factor defining possibilities for retrieving characteristics of atmospheric gas composition from measurements of outgoing thermal IR radiation spectra (including the SI-1 measurements). When the temperature vertical gradient is close to zero (for example in the presence of the temperature inversion layer), the absorption band of methane is not detectable in the spectra obtained by the SI-1 instrument in 1977 and 1979. On the basis of the analysis of brightness temperatures in different absorption bands (bands of CO ₂ at 15 μm, O ₃ at 9.6 μm and CH ₄ at 7.6 μm) the scattering diagram of amplitudes of spectral variations of outgoing radiation has been received and studied. It is shown that the SI-1 device is sensitive to natural variations of outgoing thermal radiation caused by not only CO ₂, ozone and methane variations, but also variations of such gases as H ₂O, HNO ₃ and N ₂O. The N ₂O, CFC-11 and CFC-12 contents cannot be estimated from SI-1 data without the essential spatial averaging of satellite measurements for the suppression of random measurement errors.