SPIE Proceedings [SPIE Fourth International Asia-Pacific Environmental Remote Sensing Symposium 2004: Remote Sensing of the Atmosphere, Ocean, Environment, and Space - Honolulu, HI (Monday 8 November 2004)] Passive Optical Remote Sensing of the Atmosphere and Clouds IV - Determination of CERES flight models 1 and 2 sensors zero-radiance response variability with elevation and azimuth scan angles on-orbit aboard TERRA Spacecraft