With shallow imaging the listening time and the pulse repetition period ______.

With shallow imaging the listening time and the pulse repetition period ______.

• A. Lengthen
• B. Remain the same
• C. Shorten
• D. Increase then decrease

Answer: (C)

Shallow imaging focuses on near-surface reflections, so the energy returns arrive quickly. To capture these reflections, you listen for a brief period after each shot. The interval between shots (the pulse repetition period) must be longer than the longest two-way travel time to the deepest reflector you care about; with shallower targets, that travel time is small, so the PRP can be shortened as well. By keeping both the listening time and the PRP shorter, you can fire more shots per unit time while still avoiding overlap of signals from successive shots.

Shallow imaging focuses on near-surface reflections, so the energy returns arrive quickly. To capture these reflections, you listen for a brief period after each shot. The interval between shots (the pulse repetition period) must be longer than the longest two-way travel time to the deepest reflector you care about; with shallower targets, that travel time is small, so the PRP can be shortened as well. By keeping both the listening time and the PRP shorter, you can fire more shots per unit time while still avoiding overlap of signals from successive shots.