CALCULATIONS OF ATMOSPHERIC INFRARED RADIATION AS SEEN FROM A METEOROLOGICAL SATELLITE

Abstract

Since certain constituents (water vapor, ozone, carbon dioxide, etc.) of the atmosphere have pronounced absorption and emission bands in the infrared region of the spectrum, the radiation which is radiated upward from the atmosphere will depend on the distribution and temperature of the constituents, and this radiation can be measured from meteorological satellites. This paper shows sample calculations of the emission by the water vapor in three wavelength intervals (at two places in the strong absorption band, 6.0 and 6.2 µ, and in the region of weak absorption, 8 to 13 µ). Water-vapor distributions used in these calculations are those for the United States, measured by the University of Chicago and showing rather high stratospheric humidities; for the United Kingdom, measured by the Farnboro Research Establishment and showing rather low stratospheric humidities; and for Swan Island, West Indies, where no humidity data were available above about 10 km. It is shown that, for very strong absorption by water vapor (as at 6.0 µ) and the United States humidity distribution, the upward emission originates mostly in the stratosphere, whereas, for weaker absorption or lower stratospheric humidities, the upward emission comes mostly from below the tropopause. In the water-vapor ?window? at 8 to 13 µ, about two-thirds of the upward emission in the vertical comes from the ground in middle latitudes (low humidities), but only about one-third of the surface radiation escapes in the tropics ; i.e., the ?window? is not at all transparent.