21 June 2015 Radiometric uncertainty of radiance measured with infrared cameras under variable ambient conditions
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Abstract
Radiometric calibration and non-uniformity correction are key operations in a signature measurement, which is a special challenge in the infrared range where a large number of parameters need to be characterized. The radiation hitting the camera's pixels will not only be due to the target, but will also depend on the atmosphere and optical components like lens and spectral filters. To obtain broadband radiative properties of a target, the spectral properties of these components must be accurately characterized. In addition to signal contributions from the incident radiation, the pixel’s digital numbers will also depend on the individual responses of the pixels. Results are presented for an infrared camera of the following examined parameters: stabilization period, dynamic response, dynamic range, ambient temperature dependence and non-uniformity. In radiometric calibrations using area blackbody sources, an estimate of the sensor signal is obtained by pixel averaging (which reduces the influence of non-uniformity), and the spectral distributions of the sources are known (via the Planck distribution). These conditions do not normally apply for signature measurements e.g. of small hot spots involving only a few pixels. The measurement uncertainty is compared between calibrations based on mean values and pixel-wise calibration. It is shown that the pixel-by-pixel variation should be included in an analysis of the measurement uncertainty. A discussion is given of the effects of unknown spectral distributions on the measurement uncertainty.
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Thomas Svensson, Henrik Larsson, Johan Eriksson, "Radiometric uncertainty of radiance measured with infrared cameras under variable ambient conditions", Proc. SPIE 9526, Modeling Aspects in Optical Metrology V, 95260E (21 June 2015); doi: 10.1117/12.2184861; https://doi.org/10.1117/12.2184861
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