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Optical Engineering

Dynamic electrothermal model for the Earth Radiation Budget Experiment nonscanning radiometer with applications to solar observations and evaluation of thermal noise
Author(s): Nour E. Tira; J. Robert Mahan; Robert Benjamin Lee
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Paper Abstract

A dynamic electrothermal model of the Earth Radiation Budget Experiment total, nonscanning channels has been formulated and implemented as a computer program. This model, which is a modification of an earlier version, is used to simulate two types of solar observations: those obtained through the solar port during solar calibration and those obtained during the satellite pitchover maneuver in which the sun is observed by the radiometer in its Earth-viewing configuration. New results of both simulations are compared with actual flight data. These results show an improved agreement between the simulated and observed radiometer response over previous simulations. The improvement in these severe cases justifies the modification to the model and establishes its accuracy. Thermal noise has been studied also, using a separate but related model, to evaluate its contribution to the radiative energy absorbed by the active cavity. This study has revealed that scattering of the collimated solar radiation contributes, on average, 0.071 mW during solar calibration and 0.207 mW during the pitchover maneuver. These values represent, respectively, 0.156% and 0.460% of the peak power that enters the cavity (?45 mW). On the other hand, the maximum amounts of diffuse power due to emission from the field-of-view limiter and the aperture plate are, respectively, 0.120 and 0.01 1 mW, which amount to 0.270% and 0.024% of the peak power. Finally, the cavity self-contamination contributes only 0.034 mW, or 0.071%, of the peak power absorbed by the active cavity radiometer. This study confirms the assumption that, due to the geometry of the radiometer assembly and the optical properties of its components, thermal noise is small and well within the range of previous estimates.

Paper Details

Date Published: 1 April 1990
PDF: 8 pages
Opt. Eng. 29(4) doi: 10.1117/12.55605
Published in: Optical Engineering Volume 29, Issue 4
Show Author Affiliations
Nour E. Tira, Virginia Polytechnic Institute and State Univ. (United States)
J. Robert Mahan, Virginia Polytechnic Institute and State Univ. (United States)

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