Final answer:
It is not unusual to receive a strong echo sounder return at about 200 fathoms during the day and closer to the surface at night due to diurnal vertical migration of marine organisms. The echo sounder works by measuring the time it takes for a sound to bounce back, which helps determine the ocean's depth or locate underwater objects.
Step-by-step explanation:
When using an echo sounder in deep water, it is not unusual to receive strong returns at different depths depending on the time of day. During the day, organisms that reside in deeper water might come closer to the surface at night, known as diurnal vertical migration, resulting in differing echo returns. Specifically, it is NOT unusual to receive a strong return at about 200 fathoms (366 meters) during the day, and one nearer the surface at night. The echo sounder is a device used for sonar that measures the time it takes for an emitted sound wave to bounce off a surface and return to the source, which is useful in determining the depth of the ocean or locating objects underwater.
As for the distance to an object that creates an echo, using the example where a sonar echo returns to a submarine 1.20 seconds after being emitted, we can calculate the distance using the speed of sound in seawater. To find the distance, one would multiply the time taken for the sound to return (1.20 seconds) by the speed of sound in seawater (approximately 1500 meters per second), and then divide by 2, since the echo has to travel to the object and back again.