  Eddy current stimulated thermography is an emerging technique for
non-destructive testing and evaluation of conductive materials. However,
quantitative estimation of the depth of subsurface defects in metallic
materials by thermography techniques remains challenging due to significant
lateral thermal diffusion. This work presents the application of eddy current
pulse compression thermography to detect surface and subsurface defects with
various depths in an aluminum sample. Kernel Principal Component analysis and
Low Rank Sparse modelling were used to enhance the defective area, and cross
point feature was exploited to quantitatively evaluate the defects depth. Based
on experimental results, it is shown that the crossing point feature has a
monotonic relationship with surface and subsurface defects depth, and it can
also indicate whether the defect is within or beyond the eddy current skin
depth. In addition, the comparison study between aluminum and composites in
terms of impulse response and proposed features are also presented.
