Method of comparing CERES and ScaRaB 3 measurements

The CERES Flight Model 5 was placed in orbit aboard the NPP spacecraft in October 2011 to replace the CERES FM-1 through -4 aboard the Terra and Aqua spacecraft which have provided Earth radiation budget measurement for eight to ten years. The SCAnner for RAdiation Budget (ScaRaB) 3 instrument aboard the Megha-Tropique spacecraft was put in orbit in September 2011. The CERES instruments can be rotated in azimuth so the CERES can observe the same scene in the same direction as ScaRaB, so that both instruments measure the same radiance for shortwave (reflected solar) radiance and for longwave (Earth-emitted) radiance. The data collected in this manner serves to validate all of these instruments. The geometry of the operation of CERES as constrained by the orbits is described. Special operations of CERES instruments were begun on 17 April 2012.