Reference-free interpretation of flash thermography data

Abstract

The Thermographic Signal Reconstruction (TSR) method has become a widely accepted approach to processing and interpreting active thermography data, since its introduction six years ago. Initially, the technique was used to create compact, noise-free sequences replicas of flash thermography data. Derivatives of the replica were used to obtain increased sensitivity, noise and artifact suppression, and reference-free evaluation and quantification of results. However the derivative of a single pixel time history can also be analysed without reference to adjacent pixels to detect the presence of a subsurface defect, or in the absence of a defect, it can be used to measure the local thermal diffusivity, sample thickness or defect depth. In this article, we illustrate the behaviour of the derivative in some basic cases, and show how it can be used to infer the subsurface state of a sample.