How does acoustic image give the depth information i.e. 3d?

[rednewguy]

acoustic imaging

i heard in a lecture that acoustic imaging is used in boeing inspections and dsps are used for this purpose. my doubt is how do acoustic image gives the depth information i.e. 3d view.
thanks

 

[echo47]

acoustic imaging

The sound penetrates the material and reflects from objects within. For example, an ultrasound that looks inside your body. The two-way travel time and sound velocity tells you the depth.