Atmospheric Absorption Measurements with a Microwave Radiometer
Abstract
The absorption of microwave radiation in traversing the earth's atmosphere has been measured at three wavelengths (1.00 cm, 1.25 cm, and 1.50 cm) in the region of a watervapor absorption line. The measurement employs a sensitive radiometer to detect thermal radiation from the absorbing atmosphere. The theory of such measurements and the connection between absorption and thermal radiation are presented. The measured absorption together with watervapor soundings of the atmosphere permits the calculation of the absorption coefficients at standard conditions (293°K, 1015 millibar). These are 0.011, 0.026, and 0.014 db/km/g H_{2}O/m^{3} for the wavelengths 1.00 cm, 1.25 cm, and 1.50 cm, respectively. These values are (50 percent) greater than those given by the theory of Van Vleck. The collision width of the line and its location are in better agreement with the theory and infrared absorption measurement. It is also found that there is very little (<20°K) radiation from cosmic matter at the radiometer wavelengths.
 Publication:

Physical Review
 Pub Date:
 September 1946
 DOI:
 10.1103/PhysRev.70.340
 Bibcode:
 1946PhRv...70..340D