Extrapolation of Earth-Based Solar Irradiance Measurements to Exoatmospheric Levels for Broad-Band and Selected Absorption-Band Observations

This paper describes techniques and presents results for extrapolating earth-based spectral-band measurements of directly transmitted solar irradiance to equivalent exoatmospheric signal levels. These techniques have been used to aid in determining system gain settings of the Halogen Occultation Experiment (HALOE) sunsensor system being developed for the NASA Upper Atmosphere Research Satellite (UARS) and for the Stratospheric Aerosol and Gas (SAGE) II instrument launched in October 1984, on the NASA Earth Radiation Budget Satellite (ERBS). A band transmittance approach was employed for the HALOE sunsensor, which has a broad-band channel determined bythe spectral responsivity of a silicon detector. A modified Langley plot approach, assuming a square-root law behavior for the water-vapor transmittance, was used for the SAGE II 940-nm water-vapor channel.