Absolute measurements of atmospheric emission and absorption in the range 100–1000 GHz

A spectrometer has been constructed which consists of a polarizing Michelson interferometer with a cooled detector, hot and cold reference bodies, a tilting mirror and a computerised control and data handling system. It has been used to obtain well-calibrated spectra of atmospheric emission as a function of water vapour content and zenith angle. Preliminary analysis of spectra taken at 2400m on Tenerife shows that the opacity in the millimetre wavelength windows is low, is proportional to the secant of the zenith angle under stable conditions, and is well correlated with the readings of near-i.r. hygrometers.