A CLOUDY-SKY RADIATIVE-TRANSFER MODEL SUITABLE FOR CALIBRATION OF SATELLITE SENSORS

The authors present a radiative transfer model suitable for calibration of satellite instruments sensing in the solar spectrum. The model consists of two clear layers sandwiching a plane-parallel cloud layer. Clear-sky optical effects are treated with modified Beer's Law relationships and cloud optical effects are treated with the delta-Eddington method. We use a model inversion process to determine an effective cloud optical depth from surface measurements of global irradiance and then use the model to calculate the corresponding upward irradiance at the top of the atmosphere. Upward irradiances are converted into directional radiances using empirical bidirectional reflectance factors. The model radiances are then compared to simultaneous satellite measurements of radiances from the cloud tops over the surface site.