## 3 Experiments and Discussion
### Phase Maps  
The status of phase change for defect 1 is shown through the images in Figure 10. Figure 10a-c show the interferometric fringe patterns in the cooling process after the heating gun's heating of the sample. Figure 10d-f show the wrapped phase maps derived using the proposed method at three time instants. Figure 10g-i show the wrapped phase maps at those time instants without going through the WFF filter, which has a relatively high signal to noise ratio (SNR). A video sequence illustrating the phase change corresponding to Figure 10d-f can be viewed in Video S2.  
Figure 8: (**a**) WTB sample for inspection and the delamination defects at subsurface circled in red; (**b**) Heat gun for loading the blade surface.  
Figure 9: Temperature measurement for the inspected surface during the cooling process.  
The inspection results for defect 2 are shown in Figure 11 in the same sequence as those for defect 1. Figure 11a-c show the interferometric fringe patterns at three time instants in the cooling process after the heating gun heated of the sample. Figure 11d-f show the wrapped phase maps derived using the proposed method at those time instants. Figure 11g-i show the wrapped phase maps at the same time points without going through the WFF filter. As known for this defect, the derived wrapped phase map is not as regularly shaped as defect 1 and the change of the phase map shape illustrates the defect's properties. The video sequence for illustrating the phase status change can be viewed in Video S3.  
Figure 10: Results derived at three time instants for defect 1 on the WTB; (**a–c**) Fringe patterns at time instants of 65 th frame, 130 th frame, and 200 th frame; (**d–f**) Phase maps derived with the proposed method at time instants of 65 th frame (\(\Delta\dot{\phi}_{t_{\text{5}}}\)), 130 th frame (\(\Delta\dot{\phi}_{t_{\text{130}}}\)), and 200 th frame (\(\Delta\dot{\phi}_{t_{\text{200}}}\)); (**g–i**) Phase maps without passing through WFF filter at time instants of 65 th frame (\(\Delta\dot{\phi}_{t_{\text{5}}}\)), 130 th frame (\(\Delta\dot{\phi}_{t_{\text{130}}}\)), and 200 th frame (\(\Delta\dot{\phi}_{t_{\text{200}}}\)).  
The derived wrapped phase map could also be unwrapped using ordinary phase unwrapping methods. The unwrapped phase maps for defect 1 and defect 2 are shown in Figure 12 the quality of which depends on that of the wrapped phase maps; as the SNR increases using the WFF filter, the unwrapping phase maps are without excessive noise. Figure 13 shows the cross-section profiles of defect 1 and defect 2, and this denotes the first derivative of displacement by shearography's detection, and the smoothness of the line is attributed to the WFF filtering process. Correspondingly, the 3D phase maps in Figure 14 indicate intuitively the strains for the two defects.  
Figure 11: Results derived at three time instants for defect 2 on WTB; (**a–c**) Fringe patterns corresponding to the time instants of 65 th frame, 130 th frame, and 200 th frame; (**d–f**) Phase maps derived with the proposed method at the instants of 65 th frame (\(\Delta\phi_{t_{\rm{cg}}}\)), 130 th frame (\(\Delta\phi_{t_{\rm{130}}}\)), and 200 th frame (\(\Delta\phi_{t_{\rm{200}}}\)); (**g–i**) Phase maps derived without going through WFF filter at time instants of 65 th frame (\(\Delta\phi_{t_{\rm{cg}}}\)), 130 th frame (\(\Delta\phi_{t_{\rm{130}}}\)), and 200 th frame (\(\Delta\phi_{t_{\rm{200}}}\)).  
Figure 14: 3D phase maps for **(a)** defect 1 and **(b)** defect 2.  
Figure 12: Unwrapped phase maps at **(a)** defect 1 and **(b)** defect 2.  
Figure 13: Cross-section profiles; **(a)** defect 1 **(b)** defect 2.