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27 January 1997 Use of Kirchoff's law to compensate for scan-dependent gain and polarization effects in a thermal infrared radiometer
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Abstract
Thermal infrared and microwave satellite radiometers are typically calibrate in-flight using a space view as a radiometric zero, and a view to a blackbody as a full-scale reference view. This study refers specifically to the high- resolution dynamics limb sounder, an infrared filter radiometer under development for the NASA EOS-Chem payload, but some aspects of it are of general interest for radiometric calibration. Instruments of this type typically have scan patterns generated by a plane scan mirror near the front of the optical train. The calibration views are thus acquired with a slightly different optical configuration from each other, and from the required scene views, raising questions about scan-dependent gain and polarization effects. The present paper establishes a formalism for handling polarization issues in radiometers, adapted to a geometrical ray-tracing modeling approach. Using this formalism, it is shown that the gain errors are substantially cancelled provided the scanning geometry permits a space view with a very similar optical arrangement to the required scene views, and the blackbody, intermediate mirror and scan mirror can be maintained at the same temperature. This cancellation follows from the application of Kirchoff's law, and is thus a robust conclusion. Explicit general expressions are given for the residual errors arising with non-zero temperature differences.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Christopher W. Palmer "Use of Kirchoff's law to compensate for scan-dependent gain and polarization effects in a thermal infrared radiometer", Proc. SPIE 2957, Advanced and Next-Generation Satellites II, (27 January 1997); https://doi.org/10.1117/12.265451
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