Clouds and the Earth's Radiant Energy System

[6] The first CERES instrument Proto-Flight Module (PFM) was launched aboard the NASA Tropical Rainfall Measuring Mission (TRMM) in November 1997 from Japan.

In RAP mode, the radiometers scan in elevation as they rotate in azimuth, thus acquiring radiance measurement from a wide range of viewing angles.

[13] The CERES instruments were designed to provide enhanced measurement stability and precision, however achieving and ensuring absolute accuracy over time was also known to remain as an ongoing challenge.

[14] Despite the more advanced capability of CERES to monitor Earth's TOA radiative fluxes globally and with relative accuracy, the only practical way to estimate the absolute magnitude of EEI (as of year 2020) is through an inventory of the changes of energy in the climate system.

[13] For a climate data record (CDR) mission like CERES, accuracy is of high importance and achieved for pure infrared nighttime measurements by use of a ground laboratory SI traceable blackbody to determine total and WN channel radiometric gains.

CERES onboard calibration sources intended to achieve this for channels measuring reflected sunlight include solar diffusers and tungsten lamps.

However the lamps have very little output in the important ultraviolet wavelength region where degradation is greatest and they have been seen to drift in energy by over 1.4% in ground tests, without a capability to monitor them on-orbit (Priestley et al. (2001)[20]).

The planned CLARREO Pathfinder mission aims to provide a state-of-the-art reference standard for several existing EOS instruments including CERES.

[22] A concurrent pair of studies measuring global ocean heat uptake, ice melting and sea level rise with a combination of space altimetry and gravimetry suggested similar agreements.