Which statement about PRF and depth of view is true?

Which statement about PRF and depth of view is true?

• A. PRF increases with depth of view
• B. PRF is inversely related to depth of view
• C. PRF is unrelated to depth of view
• D. PRF is determined by sound source

Answer: (B)

The main idea is that pulse repetition frequency is governed by how long echoes take to return from the deepest point you’re imaging. To avoid echoes from different pulses overlapping, the system can only fire again after the farthest echo has returned. As depth increases, that round-trip time gets longer, so the pulses must be sent less often. That makes PRF decrease as depth of view increases, i.e., PRF is inversely related to depth of view. At shallow depths you can fire more rapidly for a higher frame rate; at deeper depths you must slow down the pulse rate to prevent overlap. The other statements don’t fit because increasing PRF with depth would cause range ambiguity, PRF being unrelated ignores the travel-time limitation, and PRF being determined by the sound source doesn’t reflect how the system controls pulse timing to match depth.

The main idea is that pulse repetition frequency is governed by how long echoes take to return from the deepest point you’re imaging. To avoid echoes from different pulses overlapping, the system can only fire again after the farthest echo has returned. As depth increases, that round-trip time gets longer, so the pulses must be sent less often. That makes PRF decrease as depth of view increases, i.e., PRF is inversely related to depth of view. At shallow depths you can fire more rapidly for a higher frame rate; at deeper depths you must slow down the pulse rate to prevent overlap. The other statements don’t fit because increasing PRF with depth would cause range ambiguity, PRF being unrelated ignores the travel-time limitation, and PRF being determined by the sound source doesn’t reflect how the system controls pulse timing to match depth.