Characterization of flight model I of the Scanner for Radiation Budget (ScaRaB) instrument in the solar spectral domain

The Scanner for Radiation Budget (ScaRaB) is an instrument for the determination of Earth radiation budget parameters from space. Onboard calibration is necessary during the experiment. For this purpose, various calibration sources are integrated in the ScaRaB instrument. Before launch, all onboard sources have to be calibrated on ground. This paper deals with the ground calibration in the solar spectral domain. The ground calibration standard for the lamps is a reference diffusor which is illuminated by the sun. The absolute radiance of the diffusor is calculated from its absolute reflectivity and the incoming solar irradiance. The latter is measured with a pyrheliometer. The total error of the ground measurements of the filtered radiance of the onboard lamp sources is estimated as 1.4 to 4 percent of the nominal value. However, the lamp sources show aging effects during ground testing from 0.5 percent to 4 percent of the nominal value. (Author)