Enabling Continuity of the Earth Radiation Budget Climate Data Record using the Clouds and Earth's Radiant Energy System (CERES) Flight Model 5 instrument on S-NPP

The Clouds and Earth's Radiant Energy System (CERES) instruments measure two components of the earth's radiation budget (ERB)- the reflected solar radiation and the outgoing longwave radiation. The measurements from CERES along with data from imagers as well as meteorological and aerosol assimilation data are combined to provide a climate data record (CDR) of the ERB at the top of atmosphere, surface and various levels in the earth's atmosphere. There are currently six operational CERES instruments on board four spacecraft- Flight Models (FM) 1 and 2 are aboard the Terra spacecraft launched in December 1999, FMs 3 and 4 on Aqua launched in March 2002, FM5 on S-NPP launched in October 2011, and FM6 on NOAA-20 launched in November 2017. In order to continue the CDR as newer instruments are launched, a radiometric adjustment at the start of the mission of the new instrument is necessary to bring it to the same absolute radiometric scale as the predecessor. In this paper, we describe a process to place the S-NPP/FM5 instrument on the same radiometric scale as the Aqua/FM3 instrument in order to continue the CDR. This involves using inter-comparison data from the two instruments viewing the same earth scene simultaneously when their orbits overlap. A Lagrange multiplier objective constrainment technique is used to obtain the required adjustments to the SNPP/FM5 spectral response within measurement uncertainties to match the measurements from the Aqua/FM3 instrument. The results from various validation studies are also shown before and after these adjustments have been applied.