Sonar uses sound waves and works underwater, where radio waves are absorbed almost immediately. Radar uses radio waves and works through air and space, where they travel a long way. Both detect objects by sending a signal out and timing the echo — the difference is the medium, and the medium decides which one is usable.
The core difference
- sonar — SOund Navigation And Ranging. Sound waves, used underwater.
- radar — RAdio Detection And Ranging. Radio waves, used in air and space.
Both are acronyms that have become ordinary words, which is why neither is capitalised any more.
Why each suits its medium
Radio waves are absorbed by water within a very short distance, so radar is nearly useless below the surface. Sound, by contrast, carries extremely well through water — far better than through air. The choice is not preference, it is physics.
How they work
Both are echo-ranging: emit a pulse, wait for the reflection, and calculate distance from the delay. Bats and dolphins do the same thing biologically, which is called echolocation.
Related term
Lidar completes the set — light detection and ranging, using laser pulses. It is the technology behind much self-driving-vehicle sensing and archaeological survey.
Frequently asked questions
Why is radar not used underwater?
Radio waves are absorbed by water within a very short distance. Sound carries well through water, so sonar is used instead.
Are sonar and radar acronyms?
Yes. Sonar is Sound Navigation And Ranging; radar is Radio Detection And Ranging. Both became ordinary words and lost their capitals.
What is lidar?
Light detection and ranging — the same echo-timing principle using laser pulses, used in self-driving vehicles and archaeological survey.