Why do submarines use sonar instead of radar

Submarines were first built in the 19th century and rose to popularity during the First World War. The extraordinary capability of these vessels to remain beneath the surface of the water for long periods and enter enemy waters undetected made them indispensable in warfare.  

Apart from the navy, submarines have also found their use in marine research, where scientists use such boats to study deep-sea flora and fauna. Additionally, submarines are used in modern tourism ideas that take passengers on-board through a journey of deep-sea adventures.  

But coming back to its primary use, which is warfare, submarines have typically preferred the Sonar (sound navigation ranging) technology over Radar (radio detection and ranging) to detect enemy battleships. And now, this preference has spread to the other submarine applications as well.  

Before we dive deeper into the reasons behind this, let us first briefly look at how Radar and Sonar technologies work. Read on to know more.  

Working Principle of Radar 

Radar system typically uses electromagnetic waves to determine the presence of a distant object. It consists of an antenna that works for both the transmission and the reception of waves.  

When the transmitter sends out electromagnetic waves, they travel through a distance to strike an object, hitherto unseen. Some of these waves are then sent back to the Radar unit, where the receiving antenna detects them. The Radar continues to transmit waves and pauses in between for a few seconds to listen to returning waves.  

Whatever waves the Radar antenna can detect are sent to an electronic component that calculates the distance of the object that returned the waves based on the time the waves took to come back.  

Learn more about the advantages and disadvantages of Radar here.

Working Principle of Sonar  

The working principle of a Sonar system is similar to that of a Radar system. A Sonar system also has a transmitter and a receiver to detect the distance of an object. The major difference, however, is that while Radar systems send out electromagnetic waves, Sonar units work with sound waves.  

A portion of these sound waves, after hitting an object at a great distance, travel back to the source. Once back to the unit, the reflected sound waves are converted to electrical signals. A processor in the unit can then measure the distance of the object from the time taken for the sound waves to travel back.  

Sonar units can detect not just the presence of an object but also the hardness of the object as a pulse reflecting from a harder object produces a deeper sound.  

Reasons Submarines Prefer Sonar to Radar 

There are several reasons reflected sound is a better judge of any foreign object approaching a submarine than reflected electromagnetic waves. Here are the crucial ones. 

Radar Transmissions Get Absorbed Under Water 

Radar uses electromagnetic waves that belong to the microwave frequency. While microwaves have a wavelength range between 30 cm and 1 mm, Radar typically sends out waves of a length of about 1 cm.  

The reason behind sending out wavelengths of this range is the functioning of the unit itself. Radar works best when smaller antennas are used to send out narrow beams and the wavelengths of 1 cm suit this purpose. This process makes Radar units send out waves quickly and receive the reflections in short times.  

However, this principle, while functioning well over land, runs into trouble under the water. Microwave wavelengths get easily absorbed under the water long before they hit any target object. Most waves emitted from the Radar unit are thus, lost in the vast ocean. 

Lack of Power in Radar to Reach Larger Distances 

It is not that electromagnetic waves emitted by Radar can never reach an object at a distance. They can, but that would need an extremely powerful Radar with larger antennas.  

If a submarine was to use such a large and powerful antenna, it would have to place the antenna above the sea level. This would increase the chances of the submarine being detected by enemy ships from afar.  

In contrast, sound waves emitted from a Sonar unit can travel long distances under the water without being absorbed. There is no way for an enemy ship to locate the source of the Sonar unit as it is completely hidden underneath the surface of the ocean. 

Radar is an Active-Only System 

A Radar system must send out waves to get anything reflected. This property makes it an active system. While accuracy can be good with an active system, in warfare, it can be dangerous. Enemy warships might have sensors located on their ships that detect the presence of an active Radar transmission unit.  

A Sonar system, on the other hand, can be both active as well as passive. This means that if a submarine just chooses to listen to sound waves without transmitting any, it can do that, too. In this way, a submarine can detect the presence of other underwater objects without giving its position away. This property is helpful not just in warfare but also in marine research.  

Possibility of Jamming Radar-Emitted Waves  

With a Radar system, the possibility of jamming increases manifold. Radar jamming is an extremely successful technique in which interfering frequencies are sent to the enemy’s Radar unit so that it cannot easily detect the presence of an object. Thus, Radar units become more vulnerable when used in marine warfare.   

Sonar systems are comparatively harder to jam because it is difficult to mask the position of the Sonar unit that sends out the jamming signals. Therefore, Sonar systems are relatively safer and less prone to detection than Radar systems. 

Sonar is Lower in Cost

When it comes down to pricing, Sonar systems have a distinct advantage over Radar systems in cost-effectiveness. Even though this may not be a factor in the navy, it matters a lot when conducting scientific research.   

Researchers are always looking to cut down on costs so that they can conduct experiments within received grants. To survey the ocean floor and study the deep sea, Sonar systems work perfectly fine without pinching the pockets of the research teams.  

Also, there is no question of compromising on quality when Sonar systems are used versus Radar systems just because it is less costly. 

Sound Waves Travel at Great Speeds Under Water  

The primary reason this comparison between Radar and Sonar systems came about is that Radar systems can transmit waves at a much quicker rate than Sonar systems. As a result, electromagnetic waves that return to the Radar unit take a much shorter time than acoustic waves that return to the Sonar unit. Naturally, users would prefer a quicker system, and hence Radar must be the right choice.  

But, even if we take the speed of waves into consideration, where underwater transmission and reflection of waves are concerned, sound waves are not that much lagging in speed when compared to microwaves. This is because sound travels a lot faster under the water than it does in air. Hence, the extra speed that Radar units promise does not help much in the case of submarines. 

Takeaway 

The use of Radar systems versus Sonar systems in submarines has been evaluated and Sonar systems have been found to fare better in almost all the parameters. It is not a surprising result because underwater animals such as whales and dolphins have been known to use sonar waves to detect foreign objects or other animals ever since they existed.  

The many advantages of Sonar systems such as greater underwater speed, lesser vulnerability towards detection, passive monitoring, and identification of faraway objects make them an obvious choice for anyone who wishes to explore the deep sea in a submarine.  

Regardless of whether the submarine is being used for warfare, tourism, or research purposes, Sonar systems provide more accurate results at lower costs as compared to Radar systems. 

 

Learn More

Looking to dive deeper and learn more about submarines? “Submarine Technology for the 21st Century” is a great primer that will go into detail but without overwhelming the reader.

Check it out on Amazon here

Check out our further reading section for some great book recommendations

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