Clouds and Earth radiant energy system: an overview

The Clouds and Earth radiant energy system (CERES) instrument was first flown aboard the TRMM spacecraft whose 35° inclination orbit allowed for the collection of radiation budget data over all local times, i.e. all solar zenith angles for the latitude range. Moreover, this instrument has gathered the only bidirectional radiance data covering all local times. An additional quartet of CERES instruments are now operating in pairs on both the TERRA and AQUA spacecrafts. Thus far, these instruments have collected several years of Earth radiation budget observations and continue to operate. For each of the TERRA and AQUA spacecrafts, one CERES instrument operates in a cross-track scan mode for the purpose of mapping the EarthÕs outgoing longwave radiation and reflected solar radiation. The other operates in an azimuthal rotation while scanning also in zenith angle for the purpose of gathering measurements for the angular distribution of radiance from various scene types, to improve the computation of fluxes from radiance measurements. The CERES instruments carry in-flight calibration systems to maintain the measurement accuracy of 1% for measured radiances. In addition to retrieving fluxes at the top of the atmosphere, the CERES program uses data from other instruments aboard the spacecraft to compute the radiation balance at the surface and at levels through the atmosphere.