Flash thermography contrast model based on IR camera noise characteristics

Abstract

Flash thermography data is typically interpreted as either a sequence of images, or a collection of pixel time histories acquired after flash heating of the surface. Modelling of the process typically requires a detailed understanding of the thermophysical properties of the sample, as well as the amount of energy used to excite the sample. Often, this information is not available to the NDT practitioner. Furthermore, since flash thermography is often performed with infrared cameras that do not provide absolute temperature data, it may be difficult to correlate modelling predictions to the output of the camera. We have developed a simple model that takes into account the noise characteristics of the camera, and uses that as a basis for predicting camera response. Input energy is expressed as a multiple of noise, and can be measured from the data without the use of additional instrumentation. The method also predicts minimum detectable flaw diameters as a function of depth, noise and input energy, and provides a basis for the widely used “rule of thumb” used in thermography.