A RADIOMETRIC CALIBRATION SYSTEM FOR THE ISAMS REMOTE SOUNDING INSTRUMENT

The Improved Stratospheric and Mesospheric Sounder (ISAMS), to be flown on the Upper Atmosphere Research Satellite (UARS), will make radiometric measurements of thermal emission by a number of atmospheric gases in the intermediate (4,6-mu-m to 16,3-mu-m) infrared spectral region. In addition to relative spectral and field-of-view calibrations, an absolute radiometric determination of the integrated spectral throughput has been made using a system of two reference and one intermediate cryogenic blackbody targets. The cold reference and intermediate targets were maintained at 77 K and the variable reference target could be controlled in small steps over the range 77 K to 320 K. Calculated emissivities of order epsilon = 0,9998 could be realized for the large-aperture reference target with a structure of concentric V-grooves with diffusely emitting surfaces.