Sounding Out the Ocean's Secrets (Chinese version, 2000-2001 )

Summary: Early 19th century investigators realized that the speed of sound in water is different from its speed in air. The US Naval officers using sound to measure distance encountered problems they couldn’t explain with their limited understanding of how sound traveled in water. Using a new device called a bathythermograph, scientists mapped out the thermal layers in the ocean and studied how the speed of sound varied with the temperature and pressure of the water. Several factors including salinity, temperature, and pressure influence how far sound travels underwater. Scientists then conducted experiments to test earlier proposed theories about the bending of sound waves in seawater. In analyzing the results of these tests, they discovered a channel across which sound waves could travel thousands of miles with minimal loss of signal. The U.S. Navy exploited this to devise a system called SOSUS which allowed them to detect and get information about submarines. After the cold war ended, the Navy permitted civilian use of this device and scientists were able to learn a great deal about the geology and biology of the ocean, including the movement of whales around the world.