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

Abstract

Abstract. Advances in microbolometer long-wave infrared (LWIR) detectors have led to the common use of infrared cameras that operate without active temperature stabilization, but the response of these cameras varies with their own temperature. Therefore, obtaining quantitative data requires a calibration that compensates for these errors. This paper describes a method for stabilizing the camera's response through software processing of consecutive images of the scene and images of the camera's internal shutter. An image of the shutter is processed so that it appears as if it were viewed through the lens. The differences between the scene and the image of the shutter treated as an external blackbody are then related to the radiance or temperature of the objects in the scene. This method has been applied to two commercial LWIR cameras over a focal plane array temperature range of AE7.2°C, changing at a rate of up to AE0.5°C∕ min. During these tests, the rms variability of the camera output was reduced from AE4.0°C to AE0.26°C. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Improving the shutter-less compensation method for TEC-less microbolometer-based infrared cameras

“…In [4] the compensation of changing disturbing camera radiation has been studied based on temperature measurements inside the camera housing and using temperature-stabilized sensor arrays. Infrared cameras comprising FPAs without temperature stabilization makes the offset correction more complex since the pixel offset voltage and the radiant exitance depend on the sensor temperature (see Eqs.…”

“…The high power consumption due to the temperature stabilization is another disadvantage of these infrared cameras which lead to new correction methods. In [3,4] an approach is presented to overcome the thermal drift influences on the sensor parameters of infrared cameras without TEC. The presented correction method is based on the established shutter correction.…”

Reflective all-sky thermal infrared cloud imager

“…The infrared camera was calibrated using methods developed at Montana State University for achieving stable, radiometrically calibrated output from microbolometer cameras [33][34][35]. Additionally, the sphere reflectivity and emissivity were determined for each pixel of the allsky image by using a scanning telescope mount to rotate the sphere in front of a large-area blackbody calibration source at different blackbody temperatures and at different sphere temperatures (rotating the sphere was much easier than rotating the heavy blackbody source).…”

“…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.…”

An advanced radiometric calibration approach for uncooled thermal cameras

“…Nugent et al. (; ) set 0·5°C/min as the maximum rate of change in FPA temperature during their experiments, which is not enough for the requirement of rapidly changing FPA temperature. The latter is primarily influenced by the ambient temperature as well as camera self‐heating; it is rather common for light uncooled thermal cameras, especially when used outdoors with wind or abrupt weather changes.…”