Satellite observations of atmospheric water vapor

Observations in the spectral window at 11-12 microm, in the carbon dioxide band at 13.3-13.4 microm, and in the water vapor rotation band at 18.7-18.8 microm have been made by the satellite infrared spectrometer and the vertical temperature profile radiometer on the Nimbus 4 and NOAA-2 satellites. Combinations of radiances measured by the separate instruments have been used to infer sea-surface temperatures and mesoscale precipitable water in tropical regions. In each spectral interval, atmospheric transmittances for these analyses were constructed from continuous absorption (of unexplained origin), which is dependent upon the square of the partial pressure of water vapor and about the inverse fifth power of temperature, in addition to absorption by resonance lines. Results are consonant with those from other laboratory and atmospheric transmittance measurements, and they underline the importance of properly modeling the water-vapor continuum in calculations of atmospheric radiation in the middle infrared.