In sonar, the region where acoustic signals are not received due to refraction is called?

• A. Surface Zone
• B. Shadow Zone
• C. Shadow Range
• D. Quiet Zone

Answer: (B)

Sound speed in water changes with depth, so acoustic rays bend as they travel. When the gradient causes rays to curve away from the receiver, there isn’t any direct path from the source to that region, creating a zone where signals aren’t received—the shadow zone. This is the area where the energy is refracted elsewhere, often down into a deep channel or back up toward the surface. The other terms aren’t used to describe this phenomenon: the surface zone denotes the uppermost layer, and shadow range or quiet zone aren’t standard descriptors for this refraction effect.