There are two basic approaches to quantitative nondestructive evaluation (NDE); the first is concerned with images and the second is concerned with material properties. The objective of the first approach is to produce an exact image of a defect or anomaly in a given sample. The defect may arise in the manufacturing process or it may occur later in the service life of the sample (i. e. damage produced by impact or mishandling). Ideally, the NDE method should produce a clear image and be capable of locating the defect in lateral extent as well as depth which would allow an observer to determine the damaged volume. In the second approach, the objective is not principally to produce an image, but rather to relate some acoustic parameter with a material property parameter. As a bonus, some of the NDE techniques in this second category also produce an image of the damaged or defect area.