ISAMS is an infra-red radiometer, which observes thermal emission from the Earth's limb. The technique of pressure modulator radiometry is used to derive vertical profiles of temperature, mixing ratios of carbon monoxide (CO), water vapour (H2O), methane (CH4), ozone (O3), nitric acid (HNO3), dinitrogen pentoxide (N2O5), nitrogen dioxide (NO2) and nitrous oxide (N2O) and aerosol extinction. ISAMS was built by an instrument team based at Oxford University and launched on the Upper Atmosphere Research Satellite (UARS) on 12th September 1991 and operated until July 1992.