Figure 6.

Snapshots of wavefield (a) 49.8 $\mathsf{\mu }\mathrm{s}$, (b) 69.7 $\mathsf{\mu }\mathrm{s}$, (c) 89.6 $\mathsf{\mu }\mathrm{s}$, and (d) 129.4 $\mathsf{\mu }\mathrm{s}$ (the red rectangular area is a void defect).