Question 952Navigation General

The correct answer is D) receive a strong return at about 200 fathoms (366 meters) during the day, and one nearer the surface at night. This is because the behavior of sound waves in water can be affected by the temperature and density of the water, a phenomenon known as the thermocline. During the day, the upper layers of the water are typically warmer, causing the sound waves to bend downward, resulting in a strong return at around 200 fathoms. At night, the upper layers cool, reducing the temperature gradient, and the sound waves travel more directly, producing a stronger return closer to the surface. The other options are incorrect because A) is the opposite of the expected behavior, B) describes false echoes at a constant depth which is not the norm, and C) refers to the need for frequent recalibration, which is not necessarily the case for deep water echo sounders.