Time Resolved Infrared Radiometry for Subsurface Interface Imaging
While most thermal NDE methods concentrate on defect detection and imaging, time-resolved infrared radiometry (TRIR) [1,2,3] has also been used successfully to determine material parameters such as thermal diffusivity and thickness. This has allowed information about material structure such as presence of corrosion, porosity or voids to be obtained. In the TRIR technique, the surface temperature of a sample is monitored via infrared emission during application of a heating pulse from an optical, microwave or induction source. Smaller heating intensities result with this technique as compared to the more common short pulse methods [4,5]. Furthermore, the early time behavior in the temperature-time response allows a self calibration to be performed for each pixel in the image, thus removing emissivity and heating beam intensity variations. The development of infrared focalplane arrays with their full field imaging capabilities at high speeds and current image processing equipment allows the TRIR algorithms which have so far have been used only on single point measurements to be applied to full images.