In-situ calibration of a microbolometer camera for the study of large-scale fires

Quantitative temperature measurements of large-scale fires are of key interest to FM Global's researchers and engineers. In this study, the effectiveness of extending an uncooled fixed-integration-time IR camera's temperature range via a reduced aperture was investigated. The corresponding calibration of the focal plane array (FPA) was performed, in situ, by investigating spatially resolved radiance levels with and without the aperture present. In-the-field calibration results were compared and validated using a blackbody (epsilon = 1) source. The effect of reduced radiant intensity on the noise equivalent temperature difference (NETD) was investigated over a wide temperature range. This study shows the effective temperature extension of a fixed-integration-time (microbolometer) IR camera from 1200 degrees F (650 degrees C) to 2192 degrees F (1200 degrees C), making this camera particularly suitable for studying fires. The temperature extension was accomplished at low cost without changing the integration time of the focal plane array (FPA), removing the camera's lens, or by using a neutral density (ND) filter.