Development of Laser Heterodyne Radiometer for Monitoring Stratospheric Air Pollution

Laser heterodyne radiometers using a CO2 laser and a Pb-salt diode laser as local oscillators have been developed for the detection of the stratospheric minor constituents. Among them, sulfer bearing compounds such as OCS and SO2 are related to the formation of the stratospheric aerosols, and they are the main concern of our study. According to a direct sampling method, the mixing ratio of OCS molecules in the atmosphere has been estimated to be 0.5 ppbv at the altitude of lower than about 20km and to decrease monotonically in the upper atmosphere. Due to the small amount of the stratospheric OCS molecules, a solar occultation measurement using a balloon-borne laser heterodyne radiometer will be required for the detection. The radiometers which are described below have been constructed for a laboratory measurement and resulted in successful detection of many absorption lines in the solar spectrum around a wavelength region of 10 um.