سوال ۱۹ کنکور ارشد مهندسی مکانیک ۱۴۰۰

PART C: Reading Comprehension

PASSAGE 1 (excerpt):

What an echo sounder does is to send high frequency sound waves (outside the range of human hearing) through the water down to the ocean bottom. Sound waves will travel through water, even faster than they travel through the air, and bounce off solid objects, such as the ocean bottom. The echo sounder measures precisely how long it takes for the sound waves to be returned to the surface and determines the depth based on the rate of return. These soundings are plotted on a graph by a computer to make an "echo map" of the ocean bottom.

According to the last paragraph, how does an echo sounder operate?