The increasing use of probablistic methods, such as the Monte Carlo ray-trace (MCRT) method, in thermal radiation and optical modeling, has created a general awareness in the community of the need for a protocol to predict, to a specified level of confidence, the uncertainty of the results obtained using these methods. This paper presents such a protocol applied to models of radiometric channels used in spaced-based earth observations. It is anticipated that the same protocol, with suitable modification, may be extended to data from actual instruments. The authors and their colleagues have developed a powerful generic MCRT-based computational environment that, among other features, is capable of simulating radiative exchange among surfaces and within enclosures. As in any MCRT thermal-radiative/optical model, the spatial resolution and accuracy of the results obtained depend on the fineness of the mesh, the number of rays traced, and the accuracy of directional and spectral surface property models. The protocol presented in this paper identifies and quantifies the contribution of these factors to the ultimate uncertainty in predicted results and to their related confidence intervals.

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A new Monte-Carlo ray-trace (MCRT) environment has been created and used for the conceptual design of a next-generation radiometer for monitoring atmospheric energetics from space. A multi-band, two-mirror reflecting telescope illuminating an array of thermal detectors is under active consideration as a follow-on to the Clouds and the Earth's Radiant Energy System (CERES) instruments.' Future instruments must provide narrower spectral resolution without concomitant sacrifices in radiometric accuracy and spatial resolution. Strategies are under study for obtaining two or more spectral channels from a single telescope without significant optical cross-talk between channels. Differential filtering based on different combinations of interference filters will be used to achieve spectral separation. Filters are potential thermal noise sources because they may absorb and re-radiate varying amounts of power in response to changes in scene spectral radiance. The MCRT design environment is used here to study the optical performance of a candidate instrument.

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