Spectral line shapes for carbon dioxide in the 43-μm band

Abstract

Spectral line shapes were educed from experimental measurements of CO2 absorption. The experiments were conducted with a 40-m path and with mixtures of CO2, N2, and O2. The measurements were made in the 2400-cm−1 region of the 4.3-μm band of CO2, from which the shapes of the high-frequency wing of the CO2 lines were obtained for self-, N2-, and O2-broadening. Two methods were used. One involved expanding the line shape form factor in a series of Chebyshev polynomials. The other was an application of a method proposed by Richardson, based on the Bayes theorem in statistics, from which the form factor was obtained directly. Results from the two methods agreed closely and were tested by simulating a 5.1-km sea-level spectrum recorded at the Naval Research Laboratory, Washington, D.C.