Calibration of Thermal Imagers by Evaluation of the Entire Field-of-View

Calibration laboratories and national metrology institutes are commonly calibrating thermal imagers with equipment and procedures that were primarily developed for the calibration of optical radiation thermometers. This approach provides direct calibration results only for a small percentage of the detector elements, which are in view of a blackbody aperture. For the remaining detector elements of the thermal imager under calibration, it is assumed that they have the same characteristics. This inference may not be always true, so a new calibration procedure is presented, which evaluates not only the correction and uncertainty of the selected detector elements, but also the uniformity of all detector elements of the thermal imager. Uniformity evaluation is based on two different approaches for the evaluation of the entire field-of-view (FOV) of the thermal imager. The first approach consists of dividing the imager FOV into partial FOVs according to the available size of the blackbody aperture. Each of the partial FOVs is successively positioned in front of a blackbody aperture, and it is automatically assembled into a single result image. The idea of the second approach is to position all detector elements (entire FOV) at the same time in front of a large blackbody aperture. Experimental work and analysis of both approaches for the calibration procedure of thermal imagers are presented.