How Sensors Work
"Sonar stands for Sound Navigation and Ranging. Sonar detects sound waves that travel through water instead of air. Scientists use sonar to help map oceans. They can map the seafloor and find underwater hazards or even locate ships and shipwrecks. There are two types of sonar. Passive sonar can detect noise from ships. Military vessels use it to “listen” to the ocean. Active sonar sends out a sound signal into the water. If the sound bounces off a shipwreck, for example, it returns as an echo. The time it takes for the echo to return tells the scientists the distance to the shipwreck."