Analysis of clouds and the Earth's radiant energy system (CERES) lunar measurements

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. The CERES instrument with the three scanning thermistor bolometers 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. The four CERES instruments (Flight Models 1 through 4) aboard Earth Observing System (EOS) Terra and Aqua platforms were instrumental in conducting lunar radiance measurement on a regular basis. Moon-reflected solar radiances were measured with the shortwave sensor while both moon-reflected solar and moon-emitted longwave radiances were measured using the total sensor. The CERES sensors performed lunar measurements at various phase angles ranging from four to ten degrees before and after each full moon phase. Additional measurements were also conducted during the lunar eclipse events. The resulting filtered radiances were normalized to the mean sun-moon distance and the mean earth-moon distance. The lunar radiances measured by the sensors from all CERES instruments for a period of January 2001 to June 2007 were analyzed and compared. The CERES total sensor results showed a variation of about +/- 0.5 percent, while a +/- 2.0 percent variation was seen in shortwave sensor results.