A smooth flat discontinuity whose major plane is not perpendicular to the direction of sound propagation may be indicated by:

• A. An echo amplitude comparable in magnitude to the back surface reflection
• B. A complete loss of back surface reflection
• C. An echo amplitude larger in magnitude than the back surface reflection
• D. All of the above

Answer: (D)

When a smooth flat discontinuity is angled relative to the sound beam, it still reflects energy, but the direction of that reflection depends on the incidence angle. If the plane isn’t perpendicular, much of the energy is steered away from the back surface, so the back-wall echo can be reduced or even vanish. At the same time, energy can reflect off the angled plane back toward the transducer, producing an echo whose amplitude may be similar to the back-surface reflection or even larger, depending on the exact geometry and impedance contrasts. Because the orientation can produce any of these outcomes, all of the above is possible.