A parametric study of the radiative and optical characteristics of a scanning radiometer for Earth Radiation Budget applications using the Monte-Carlo method

Abstract

The Earth Radiation Budget Experiment (ERBE) and the Clouds and Earth's Radiant Energy System (CERES) are systems that measure the earth's radiation budget, or the difference between earth-emitted radiation and radiation absorbed from the sun. Both these systems use three scanning radiometers based on a Cassegrain telescope design. Each of the three radiometers is sensitive in one of three wavelength intervals: shortwave, longwave, and total. A numerical model has been developed to investigate the radiative and optical characteristics of these instruments. The Monte-Carlo ray-trace method has been applied to the ERBE and CERES scanning radiometer instruments to calculate radiation exchange. In a radiative analysis, the surfaces of both instruments are found to emit a significant amount of radiation to the detector. In an optics analysis, both the ERBE and CERES instrument are found to have excellent directional selectivity. The field-of-view limits in the design of both instruments are verified using results from the optical analysis.