Ground-based millimeter-wave observations of water vapor emission (183 GHz) at Atacama, Chile

Abstract We report the first results of ground-based millimeter-wave measurements of 183 GHz atmospheric water vapor spectra from Atacama highland (4800 m alt.), Chile. The measurements were carried out in December 2005 by using a spectroscopic radiometer equipped with a superconductive heterodyne receiver. A conspicuous H 2 O spectrum at 183 GHz was detected with an integration time of only 1.5 min, and this is the first high frequency-resolution H 2 O spectrum at 183 GHz obtained in the southern subtropical region. The vertical profile of H 2 O volume mixing ratio between 40 and 64 km were retrieved from the spectrum by using the modified optimal estimation method.