An optical model for contamination effects has been developed for the Stratospheric Aerosol and Gas Experiment II/Earth Radiation Budget Satellite (SAGE II/ERBS) instrument. This model describes throughput efficiency and response characteristics as a function of molecular contamination thick-ness for indexes of refraction representative of Shuttle/ERBS/SAGE II contam-inants at seven spectral wavelengths between 0.385 and 1.02 Am. Con-tamination effects are treated as thin-film coatings on selected optical elements that cause changes in those elements' reflection/transmission/absorption characteristics. SAGE/Applications Explorer Mission (AEM) in-orbit perfor-mance data were used to estimate the optical constants for the contaminants. SAGE and SAGE II are radiometers that spatially scan the sun through the earth's atmosphere with a narrow field of view in spectral intervals from visible to the near-infrared.