Sonar: what is it, principle of operation and areas of application

When you hear the word “sonar,” your memory often comes to mind of scenes from submarine movies, where operators listen intently to the characteristic squeak, trying to detect the enemy in the dark ocean. However echolocation - this is not just a cinematic cliche, but a fundamental technology, without which modern navigation, oceanography and even amateur fishing would be impossible. The principle underlying this device was “seen” from nature, where dolphins and bats use sound waves to navigate in space long before humans appeared.

In a broad sense, sonar is a method of studying and detecting various objects in water using acoustic radiation and recording signals reflected from these objects. The key difference between sonar and radar is the propagation medium: radio waves in water attenuate almost instantly, while sound travels vast distances. That is why, when it comes to the underwater world, acoustic waves replace electromagnetic waves.

Understanding what sonar is, it is important to understand that we are talking about a complex system that turns invisible sound vibrations into a clear visual image on the screen or into a sound signal for the operator. From simple echo sounders on kleinen boats to giant sonar systems on warships, they all operate on the same physical base, although their tasks may be radically different.

Physical basis and principle of echolocation

The fundamental operating principle of any sonar is echolocation. The device emits a short pulse of a sound wave of a certain frequency into the aquatic environment. When encountering an obstacle in its path - be it a school of fish, the ocean floor, a sunken ship or an enemy submarine - the sound wave is reflected from it and returns back to the source. Hydrophone, which is the receiving element of the system, picks up this echo.

The time elapsed between the moment the pulse is emitted and the moment the reflected signal is received allows you to calculate the distance to the object. Since the speed of sound in water is a relatively constant value (albeit dependent on temperature, salinity and pressure), the formula for calculating the distance is simple and effective. Modern digital processors perform these calculations thousands of times per second, creating a dynamic picture of the surrounding space.

However, sound in water behaves more complexly than light in air. Its distribution is influenced by many factors that the operator or system automation must take into account:

• 🌊 Temperature jumps: Layers of water of different temperatures can bend the sound beam, creating “dead zones.”
• 🧂 Salinity: Changing the density of water affects the speed of the wave.
• 🐟 Biological noises: The movement of schools of fish or marine life may cause disturbances.

History of the development of acoustic systems

The idea of using sound to navigate underwater is not new. Back in 1490, Leonardo da Vinci described a method of listening to ships by lowering a pipe into the water. However, the development of technology began in the 20th century, spurred by tragedy. Collision with an iceberg and death Titanic in 1912 became a powerful catalyst for the search for ways to detect underwater obstacles.

The first practical results were obtained by the French physicist Paul Langevin during the First World War. He created the first active sonar to detect German submarines. Used then piezoelectric effect made it possible to generate ultrasonic frequencies inaudible to the human ear, but perfectly propagating in the aquatic environment.

⚠️ Warning: Early sonar models used frequencies that could disorient marine mammals, leading to modern environmental standards for the use of sonar.

During World War II, the development of sonar (then often called ASDIC) advanced greatly. There was a need not only to detect an object, but also to determine its course, speed and even type. After the war, technology migrated to the civilian sector, giving impetus to the development of commercial fishing and oceanographic research.

Sonar classification: active and passive

All hydroacoustic systems are divided into two main classes depending on the method of operation. Understanding this difference is critical to proper use of the equipment.

Active sonars work on the principle of “shout and hear an echo.” They themselves generate a sound impulse and catch its reflection. This allows you to accurately determine the distance to an object. However, this approach has a significant disadvantage: by emitting a signal, the ship or device “unmasks” itself. Anyone who has a receiver will understand that someone is “shining” sonar in this place.

Passive sonars they don't emit anything. They just listen. Their task is to catch the sounds made by the objects themselves: the noise of ship propellers, the operation of mechanisms, the voices of sea inhabitants. Passive mode is ideal for covert surveillance, but it does not provide accurate range information without the use of complex triangulation techniques with multiple receivers.

Characteristics	Active sonar	Passive sonar
Signal emission	Yes	No
Distance determination	Accurate	Difficult (requires analysis)
Stealth	Low	High
Dependence on object noise	Doesn't depend	Complete dependence

Modern systems often use a hybrid approach, when the device operates in passive mode most of the time, switching to active mode only to clarify the coordinates of the target before an attack or maneuver.

Gradient sonar and side scan

Specialized types of sonars deserve special attention, which allow you to “see” not only what is directly under the keel, but also to the sides. Side sonar (Side-scan sonar) is towed behind the vessel or mounted on its sides. It sends fan-shaped pulses outward, creating a detailed photo-like image of the bottom.

Such systems are indispensable when searching for sunken objects, laying cables or pipelines, as well as in archaeology. The image is formed based on the intensity of the reflected signal: hard objects produce a bright echo, while soft mud absorbs sound.

Gradient sonars are used to measure changes in the speed of sound in water with depth. This is critical for the correct operation of other hydroacoustic systems, as it allows the construction of accurate sound profiles of the ocean.

Why is the side sonar image sometimes distorted?

Distortion occurs due to changes in the speed of sound in different layers of water (refraction). The beam is bent, and the object is not displayed where it is in reality. For correction, complex mathematical models of the environment are used.

Applications of sonars in the civil sphere

While the use of sonar is widely known, the civilian sector is using these technologies even more actively and diversified. Fishing is one of the main industries. Fishing vessels use multibeam echo sounders to assess fish stocks, determine the density of schools and even species composition (by the nature of the reflection of the swim bladder).

In navigation, echo sounders (fathometers) are mandatory equipment for any vessel. They prevent grounding by allowing the captain to see the bottom topography in real time. Compact models integrated with chart plotters have been created for yachtsmen and boat owners.

Oceanography and geology use seabed profilers to study the structure of the seafloor, search for minerals and study tectonic processes. Scientists can “look” hundreds of meters deep into bottom sediments by sending high-power, low-frequency pulses.

• 🎣 Sport fishing: portable echo sounders help you find edges and holes.
• 🚢 Port operations: control of fairway depths and detection of underwater obstacles.
• 🏗️ Construction: inspection of bridge supports and underwater structures.

⚠️ Attention: When using high-power industrial sonars near spawning or aggregation sites of marine mammals, special environmental protocols must be followed to avoid harm to fauna.

Prospects for the development of hydroacoustics

Technologies do not stand still. Modern digital sonar - this is no longer just a “beeper”, but a complex computing complex. The introduction of artificial intelligence makes it possible to automatically classify targets, filter out interference from waves, and even recognize specific species of fish or types of ships by acoustic signature.

The direction of three-dimensional echolocation is being developed, creating three-dimensional models of underwater space in real time. This opens up new horizons for underwater robotics and autonomous vehicles that can navigate in complete darkness without human intervention.

There is also development in the field of optical sonars (lidars for water), which, although have a shorter range due to light scattering, provide incredible image detail at short distances, which is useful for diving and structural inspection.

Thus, answering the question “sonar - what is it,” we see a wide range of devices, from simple depth meters to the most complex national security systems. Regardless of complexity, they all serve the same goal - to make the invisible underwater world understandable and accessible to humans.

What is the main difference between a fish finder and a sonar?

Technically, a fish finder is a simplified form of sonar that points straight down to measure depth. Sonar is a more general term that denotes systems that can scan the space around them, determine the direction to an object and its characteristics, and not just the distance to the bottom.

Can sonar work in the air?

Theoretically, sound waves also propagate in air, but the efficiency will be extremely low due to large energy losses and high noise levels. For air, radio waves (radar) or light (lidar) are used.

Is sonar harmful to humans?

Civilian echo sounders and fishing sonars are absolutely safe for humans. Powerful military or industrial emitters at close range can affect the hearing aid or cause discomfort, but it is almost impossible for an ordinary person to be in the water near a working sonar.

Why doesn't the sonar show fish lying on the bottom?

This phenomenon is called the “dead zone” or shadow cone. If the fish lies tightly on the bottom, the echo signal from it merges with the signal from the bottom, and the processor cannot separate them. Detecting such fish requires sonar with a very high frequency and narrow beam.