Correcting for focal-plane-array temperature dependence in microbolometer infrared cameras lacking thermal stabilization

Abstract

Abstract. Advances in microbolometer detectors have led to the development of infrared cameras that operate without active temperature stabilization. The response of these cameras varies with the temperature of the camera's focal plane array (FPA). This paper describes a method for stabilizing the camera's response through software processing. This stabilization is based on the difference between the camera's response at a measured temperature and at a reference temperature. This paper presents the mathematical basis for such a correction and demonstrates the resulting accuracy when applied to a commercially available longwave infrared camera. The stabilized camera was then radiometrically calibrated so that the digital response from the camera could be related to the radiance or temperature of objects in the scene. For FPA temperature deviations within AE7.2°C changing by 0.5°C∕ min, this method produced a camera calibration with spatial-temporal rms variability of 0.21°C, yielding a total calibration uncertainty of 0.38°C limited primarily by the 0.32°C uncertainty in the blackbody source emissivity and temperature.

Radiometric calibration of infrared imagers using an internal shutter as an equivalent external blackbody

“…This suggests that the temperature-induced changes in the lens could be tracked using the FPA temperature for small lenses, while this no longer held true with larger lenses. Finally, we note that this method compares well with the method we published previously, 22,23 which is based on characterizing the changing response as a function of camera temperature. The temperature-responsecompensation method 22,23 generally produces smaller errors over time than the shutter-based method alone, but it is computationally more intensive and tends to increase the spatial uncertainty of the sensor.…”

“…Finally, we note that this method compares well with the method we published previously, 22,23 which is based on characterizing the changing response as a function of camera temperature. The temperature-responsecompensation method 22,23 generally produces smaller errors over time than the shutter-based method alone, but it is computationally more intensive and tends to increase the spatial uncertainty of the sensor. For comparison, use of the earlier published method with the same test data that produced an uncertainty in time of 0.24°C and an uncertainty in space of 0.04°C (total of 0.26°C) shown in this paper, produced an uncertainty of 0.12°C in time and 0.19°C in space (total of 0.22°C).…”

“…This method is computationally simpler than a previously published method that relies on characterizing the camera response as a function of camera temperature. 21 The previous method is essentially the same as including the nonzero temperature-dependent gain discussed in this paper, but without the use of an internal shutter. Use of the shutter method alone simplifies the real-time calibration, but as mentioned at the end of Sec.…”

“…We previously described a method that relies on characterizing the camera's response over a range of camera temperatures, 21,22 and in this paper, we describe a method that can be used in combination with or in place of that method. The method described here provides a real-time update to the radiometric calibration by using the camera's internal shutter as an equivalent blackbody source.…”

Use of Miniature Thermal Cameras for Detection of Physiological Stress in Conifers

“…Typically, this would be performed by measuring the output digital numbers while the camera views one or more blackbody sources [37]. In this study, the non-uniformity across the image was corrected using a two-point calibration technique [38], which requires measuring a blackbody at two distinct and known temperatures.…”