Doppler shift effects on infrared band models

Band-model calculations typically are employed in the analysis of low-spectral-resolution radiometer, photometer, and spectrometer measurements of hot-gas emission and absorption. Although they are not used to compute the profiles of individual lines directly, nevertheless, band models are sensitive to line shape. This line-shape sensitivity causes the net band-model emission and absorption to be sensitive to Doppler shift effects. This paper reviews the treatment of Doppler shifts on a Voigt profile spectral line, and then generalizes this result to the curve of growth, i.e., equivalent width, for both single-line and infrared band models. Finally, a synthetic spectrum for the COi 4.3-ji band is computed with and without Doppler shifts to illustrate the magnitude of the effect. It is found that band-model computations are unaffected by Doppler shift in the limiting cases of small and large absorber amounts. In the case of intermediate absorber amounts, significant effects are predicted for hypersonic flows.