Hans J. Liebe

Abstract:

Absolute attenuation rates due to water vapor and moist nitrogen have been measured in the laboratory at 138 GHz, 282 and 300 K, pressures up to 1.5 atm, and relative humidities from 80 to 100 percent. The computer-controlled measuring system is comprised of a millimeter wave resonance spectrometer (0.15 km effective path length) and a humidity simulator. Several shortcomings of earlier measurement attempts have been rectified. The data are interpreted as a water vapor continuum spectrum consisting of two terms, namely strong self-broadening (H₂O–H₂O) plus foreign-gas-broadening (H₂O–N₂) contributions. Implications of the new results for modeling atmospheric EHF window transparencies and for revising established H₂O line broadening theory are discussed.

The work was supported in part by the U.S. Army Research Office under Contract AR0 101-83.

Keywords: millimeter wave; atmospheric radio wave propagation; high-humidity spectrometer; millimeter wavelength region; water vapor continuum absorption

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