Current radiometric calibration procedures for thermal imaging cameras are usually performed for a single calibration geometry. The uncertainty estimated from such procedure only represents the calibration scenario and does not account for variation of the emitting source's size; this is known as the size-of-source effect (SSE). In this work, the measurements of the SSE for four thermal imaging cameras (two in the long-wavelength and two in the middle-wavelength infrared range) are presented. The investigation shows that the SSE is smaller for the middle-wavelength cameras.

Active infrared thermography has demonstrated an ability to retrieve critical sub-surface level information relevant to historical conservation efforts aiming to better understand and preserve multi-layered panel paintings. Complementary use of two Telops infrared cameras (Mid and Long Wave IR), a pulsed thermography system, and pulsed phase thermography processing software, has shown an ability to detect underlying drawings and pentimenti [1]. Further developments on this work have now shown an ability to detect structural components in situ, and preparatory surface irregularity across canvas layers. This non-destructive approach provides critical information to art preservationists and should be considered for broader adoption.

The theoretical and experimental results of applying a new method of infrared (IR) thermography nondestructive testing (NDT) based on the combination of optical heating and forced convection cooling are described. A properly chosen combination of two types of thermal stimulation has allowed to increase temperature contrasts in defect areas and reduce thermal loading on the samples. The 3D model of a scanning thermal flaw detector implementing the proposed inspection technique is presented.