Light and radar do not get far in water. Sound does. That is why sonar — short for Sound Navigation and Ranging — is one of the most useful tools for exploring and mapping the ocean. It uses sound waves to "see" underwater.
What NOAA uses it for
NOAA scientists use sonar mainly to:
- make nautical charts
- find underwater hazards to navigation
- search for and map objects on the seafloor, such as shipwrecks
- map the seafloor itself
Active sonar: send a ping, hear the echo
Active sonar transducers send a pulse of sound into the water. If something is in its path, the sound bounces off and returns as an echo. A transducer that can receive signals measures the strength of the echo, and from the time between sending the pulse and hearing it return, it works out the object's range and orientation.
Passive sonar: just listen
Passive sonar sends out nothing; it only detects sound coming toward it. It is used mainly to pick up noise from submarines, ships and marine animals such as whales. Staying silent is an advantage for military vessels that do not want to be found, and for scientific missions that want to listen quietly to the ocean.
The trade-off is that a single passive sonar cannot measure how far away a sound source is. That takes several passive listening devices working together, which can triangulate the source.
Sources
Based on "What is sonar?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
许可协议： CC0 1.0（公有领域） · 改编自 oceanservice.noaa.gov
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