Thermographic Nondestructive Evaluation: Data Inversion Procedures Part I: 1-D Analysis

A data inversion procedure is presented, for the one-dimensional case, to retrieve the subsurface defect depth and thermal resistance from the time evolution of the surface temperature distribution as recorded by a thermographic camera (thermal “defectometry”). The inversion algorithm is based on the global minimization of a specific functional (nonlinear least squares problem) through an iterational routine taking into account simultaneously all of the defect variables and their effects on the values of the observable parameters. Surface losses are included as an unknown Biot number in the inversion routine. This paper deals with one-dimensional thermal flow. Part II, in this same issue, covers the two-dimensional theory and the experimental results.