Calibration of uncooled LWIR microbolometer imagers to enable long-term field deployment

Abstract

Radiometric calibration methods are described that enable long-term deployment of uncooled microbolometer infrared imagers without on-board calibration sources. These methods involve tracking the focal-plane-array and/or camera-body temperatures and compensating for the changing camera response. The compensation is derived from laboratory measurements with the camera viewing a blackbody source while the camera temperature is varied in a thermal chamber. Results demonstrate absolute temperature uncertainty of ≤0.35 °C in a 24-hour period, with more than half of the uncertainty inherent in the blackbody source to which the data are compared. Although this work was driven by environmental remote sensing applications, the methods are relevant to a wide range of infrared imaging applications.

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).…”

“…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.…”

Reflective all-sky thermal infrared cloud imager

“…Our Infrared Cloud Imager (ICI) systems are based on uncooled thermal imagers that combine microbolometer detectors with advanced radiometric calibration algorithms [14,15,[33][34][35] and radiometric image processing to compensate for the atmosphere and calculate cloud fraction and products such as cloud emissivity, optical depth, and attenuation [14,15,23,36,37]. This paper describes a reflective all-sky Infrared Cloud Imager (ICI) system that uses a metal sphere to reflect the full sky into a low-cost, weather-proof microbolometer camera positioned off axis to allow for an unobstructed view of the zenith sky.…”

Photonics in nature: Yellowstone National Park in IR

“…Off the shelf, these cameras come mostly without highly accurate radiometric calibration. However, we have developed methods of calibrating these cameras and stabilizing their output to be largely independent of variations in the camera temperature [10,11]. Such calibrations have been applied to the images shown here, which produce much more uniform and quantitatively useful images than would be obtained otherwise.…”