Accurate models are needed to represent both the local lines and the continuum absorption in spectral ranges of interest. Additionally, accurate experimental data are needed, under different conditions of pressure and temperature, to test the validity of various models. Experimental data are obtained from a BOMEM fourier transform spectrometer (FTS) with a high pressure-high temperature cell and a 10-m white cell. Absorption coefficients are determined for gas mixtures (H2O, CO2, N2, O2) for pressure up to 60 atm and temperatures up to 600 K. At high pressure, the Lorentzian approach fails, and semi- empirical models are used to represent local line and far wing phenomena. The far wing nature of the line shape theory of Birnbaum is used to represent the water vapor continuum. Comparisons are made between our experimental data and synthetic spectra based on the HITRAN data base and Birnbaum's line shape for several atmospheric transmission window regions. Implications concerning atmospheric propagation are emphasized
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Measurements of water vapor continuum absorption in the 3.5-4.0-gm region are presented. The measurements were made with both long-path absorption cell and spectrophone systems. A deuterium fluoride grating tunable laser was the ir source. Measurements were made at 231C and 65 C with 14.3 Torr and 65 Torr of water vapor, respectively, buffered to 760-Torr total pressure by an 80/20 mixture of N2 /0 2. Both natural water and a special sample of deuterium depleted water (one-fiftieth the normal concentration) were used. The 65°C results agree with previous measurements by other workers. The 23°C results indicate a continuum absorption at this temperature about a factor of 2 larger than expected based on the extrapolation scheme and high-temperature data (265°C) of others.
