Sequential method for thermal diffusivity discrimination by infrared thermography: application to the use of an uncooled plane-array camera

A one-dimensional transient flash method based on an infrared thermography device permits retrieval of the thermal diffusivity map. However, each pixel of the temperature image presents a very noisy temporal signal. Moreover, in the case of an uncooled focal-plane-array camera, each plane-array detector presents independent calibration coefficients and independent offset levels. An identification method is presented which is based on the estimation of thermal diffusivity variations around a nominal value by an asymptotic gradient development. This method has the advantage of being an optimal discrimination method in the linear least-squares sense. Moreover. the diffusivity variation parameter is not correlated with the calibration parameter of each detector. Thus, the identification algorithm can be used without previous calibration of the camera. Various theoretical results are presented, illustrating the noisy temporal signal propagation in the parameter estimation, in order to show that this method can be used with a cheap thermal imaging camera. Some experimental results obtained with an uncooled thermal imaging camera, the PalmIR 250 (Raytheon) with a plane array of 320 × 240 uncooled ferroelectric detectors, are presented.