I learned this today. Radar works by using radio waves to work out the position of objects relative to the detector and sonar uses sound waves.
Radar works in a similar way to sonar, but it is far more effective in air. A sonar system sends out a sound and waits for the sound to be reflected back. By knowing how long the sound took to return, the sonar machine can tell how far away the item is. The word sonar comes from sound navigation and ranging.
Radar uses radio waves to do the same thing. Radio waves are sent out in a pulse. The radar detector waits for the radio wave to be reflected back and calculates the distance based on that. Radar stands for radio detecting and ranging.
One of the main differences between sonar and radar is the speed and distance that they can detect. This is also a reason why they are used in different medium. In air, a sound wave travels at 343 m/s. The surface area of a sound wave increases as a square of its distance, so the energy decreases as a square of its distance too. Sonar is generally at 235 decibels, so, its distance in air is limited. Radio waves are part of the electromagnetic spectrum, and they travel at the speed of light. There are no limits to how far a radio wave can travel. There are limits to how far radar can detect, though. There generally needs to be line of site to the thing being detected. If there are objects in the way, such as mountains, it will hinder the radar. The horizon can be a problem as well because the Earth curves away while the radio wave goes straight. There are radar systems that get around this by bouncing a radio wave off the ionosphere. They are called over-the-horizon radar systems. So, depending on the radar system, radar can see very far. This is why above ground detection systems are almost always radar.
However, underwater is a completely different story. The radio waves that are used in radar are microwaves, which means they are about one centimeter in wavelength. One of the properties of sea water is that it strongly absorbs microwaves, making radar useless underwater. Sonar, on the other hand, is a completely different matter. Sound waves may not travel far through air, but they travel very far and very quickly through water. The speed of sound in the ocean is about 1,500 m/s and sound waves can travel for hundreds, if not thousands of kilometers in the ocean without losing any energy. That is why airplanes use radar and submarines use sonar.
There are two types of radar and sonar. These are active and passive. With the active version, a radio wave or a sound wave is sent out and the detector waits for the reflected wave. With a passive system, the detector just listens for radio waves or sound waves coming in. A submarine in the sea might use a passive sonar because they want to hear what vessels are around them without giving away their position. SETI uses a passive radar system to listen for radio waves coming from space. They don’t want to give away our position by sending out a signal. (Plus, it could take millions of years for the reflected wave to come back.)
Sonar was invented after the Titanic sank in 1912. The idea that sounds could travel further in water has been around for a long time and some lighthouses used to use a bell under the water to warn ships. Different sonar systems were patented in 1913. A Canadian called Reginald Fessenden was the first person to use a sonar system on a submarine. The 1st World War brought a lot more research money to sonar when people realized that submarines were going to play a major part in the war.
The idea that radio waves could be reflected off an object was demonstrated by Heinrich Hertz in 1886. Alexander Popov realized that the system could be used for detecting ships when he was using it to communicate between two ships in 1897. A third ship sailed between the ships and his equipment registered it. In the 1st World War, Robert Watson-Watt used basic radio waves to give advance warning of approaching aircraft. There was some research between the wars but it was in the Second World War that many advances were made. Watson-Watt was put in charge of the program in Britain and his team had working radar by 1935. After a few more advances, it became instrumental in protecting Britain during the Battle of Britain. Without radar, and advance warning of where enemy aircraft were, Britain would not have been able to defend her skies and would probably have lost the Battle of Britain, possibly even the whole Second World War.
So, sonar is a system that uses sound waves to judge the distance to an object. It works best underwater. Radar uses radio waves for the same purpose and works best in the air. And this is what I learned today.
Photo by superphoto.be: https://www.pexels.com/photo/black-jet-plane-in-mid-air-9603038/ & by Dženis Hasanica: https://www.pexels.com/photo/photo-of-an-una-class-submarine-8577462/
Sources:
https://en.wikipedia.org/wiki/Radar
http://www.bom.gov.au/australia/radar/about/what_is_radar.shtml
https://silencewiki.com/noise-basics/how-far-does-sound-travel-the-science-of-acoustics/
https://en.wikipedia.org/wiki/Sonar
http://www4.hcmut.edu.vn/~huynhqlinh/olympicvl/tailieu/physlink_askexpert/ae456.cfm.htm