Infrared Transmission of Synthetic Atmospheres* I Instrumentation

Abstract

A technique for investigation of the infrared absorption of water vapor and carbon dioxide under simulated atmospheric conditions has been developed. The “total absorption” or area under the curve giving fractional absorption as a function of frequency can be determined for each spectral region in which characteristic absorption occurs. The apparatus includes a 22-m multiple-traversal absorption cell which permits controlled variation of the following parameters: (1) geometrical path length, (2) pressure of absorbing gas, (3) pressure of the nonabsorbing gases nitrogen and oxygen, and (4) the temperature of the gaseous mixture. A prism spectrometer is used to measure fractional absorption as a function of frequency under various experimental conditions. Although the observed shape of a given absorption band depends upon the effective slit widths of the spectrometer, the total absorption of a band depends, within wide limits, only on the foregoing listed parameters. For the range of temperatures encountered in the lower atmosphere, the influence of temperature variation on total absorption is so small that it can be neglected. On the basis of results obtained by the techniques described, it is possible to make accurate predictions of absorption of infrared radiation in the earth’s atmosphere.