Solar radiation enters the Earth's atmosphere with a portion being scattered by clouds and aerosols.

Processing, archiving and distributing Earth science data
at the NASA Langley Research Center

What are Cross-Track, Fixed and Rotating Azimuth Plane Scan modes?

Fixed Azimuth Plane Scanning (FAPS) has scan lines perpendicular to the path of the satellite, while Rotating Azimuth Plane Scan (RAPS) lines are at a wide range of angles with respect to the satellite's path. An instrument operating in RAPS has increased spectral darkening of the transmissive optics. The Cross-Track instrument is recommended by CERES, since the spatial distribution of footprints is uniform.