A limb sounding instrument that was first flown as a Small Applications Explorer Mission in 1979. Since this initial mission, a series of SAGE instruments have been flown on a variety of satellites. In all cases, the SAGE instruments measure vertical profiles of aerosol and gas concentrations by measuring the extinction of sunlight during satellite sunrises and sunsets. SAGE II was launched in October 1984 on the ERBS, and SAGE III will be flown on a number of satellites as part of NASA's EOS program. Current plans call for placing SAGE III on a Russian Meteor platform, as well as on the International Space Station.