Improved stratospheric and mesospheric sounder on the Upper Atmosphere Research Satellite

The improved stratospheric and mesospheric sounder (ISAMS) is one of the instruments on the NASA Upper Atmosphere Research Satellite which was launched in September 1991. ISAMS is a limb-viewing infrared radiometer which measures thermal emission in 24 pass bands (some of which are obtained by gas correlation). This enables the daily mapping over much of the Earth of temperature, the concentrations of 8 chemical species (water vapor, methane, ozone, nitric acid, nitrogen dioxide, nitric oxide, dinitrogen pentoxide, carbon monoxide), and aerosol opacity in the stratosphere and mesosphere. The instrument has eight separate focal planes, each consisting of a 4-element detector array, which are cooled by two mechanical coolers developed specifically for the instrument. The instrument uses a moveable mirror to scan the limb in elevation and to view at a variable azimuth angle to avoid Doppler shifts; the view may be to either side of the spacecraft in order to improve the geographical coverage.