Radiometric stability results of clouds and the Earth's radiant energy system (CERES) instrument sensors aboard EOS Terra and Aqua spacecraft

Abstract

Clouds and the Earth's Radiant Energy System (CERES) instruments were designed to measure the reflected shortwave and emitted longwave radiances of the Earth's radiation budget and to investigate the cloud interactions with global radiances for the long-term monitoring of Earth's climate. CERES instrument has three scanning thermistor bolometers that measure broadband radiances in the shortwave (0.3 to 5.0 micrometer), total (0.3 to >100 micrometer) and 8 - 12 micrometer water vapor window regions. Four CERES instruments (Flight Models1 through 4) are flying aboard EOS Terra and Aqua platforms with two instruments aboard each spacecraft. The pre-launch accuracy requirements for CERES were 1.0% in the shortwave and 0.5% in longwave regions. The in-flight calibration of CERES sensors are carried out using the internal calibration module (ICM) comprising of blackbody sources and tungsten lamp, and a solar diffuser plate known as the Mirror Attenuator Mosaic (MAM). The ICM and MAM calibration results are instrumental in understanding the ground to flight shift and in-flight drifts in CERES sensors' gains. Inter and intra instrument validation studies are conducted on the CERES measurements to monitor the behavior of the sensors in various spectral regions. Targets such as deep convective clouds and tropical ocean are used to evaluate the sensors' stability within an instrument. With two CERES instruments on same platform, inter comparison of similar sensor measurements viewing the same geolocation are also conducted. The results from these individual studies have collectively given an understanding of each CERES sensor's behavior in different spectral regions. This paper discusses the results from each of these studies which facilitated the correction of CERES data products with a calibration stability better than 0.2%. Keywords: CERES, EOS Instrument, Radiometry, Calibration, Validationt