Earth radiation budget instruments (RBI) are devices designed to study global climate change. These instruments use telescopes mounted on low earth orbit satellites to measure emitted and reflected solar radiation from the earth. Radiation is measured by virtue of temperature changes caused by absorbed radiation from the earth scans on the surface of a delicate gold-black detector. In this paper a thermal model of the detector in a typical radiation budget instrument is formulated.

A numerical solution is developed using a complex model building procedure. The idea is to split complex physical processes into simpler, individual physical processes. The basic procedure is to solve for each individual physical process in a numerically stable and efficient manner, and then assemble these processes in a cascading sequence to form a complete numerical solution of a complex model. The major advantage is that complicated mathematical models can be solved as a sequence of much simpler and less computationally intensive processes.

Parameter studies are performed on the numerical accuracy, conduction effects, initial conditions, boundary conditions due to contact with adjoining surfaces, radiation exchange with surfaces optically visible to the detector, and the volumetric heat source due to absorbed radiation from the earth scene. Extremely accurate temperature predictions are required due to the low signal to noise ratio. It is found that predictions are most sensitive to the amount and distribution of irradiation on the detector surface, which is computed independently using a Monte Carlo ray trace method.

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