What Is An Echo Sounder?

What Is An Echo Sounder?

Available ocean depth, the distance from mean water level to the seabed, is the basic criterion to consider. Estimating the depth of the seabed is crucial for safe ship navigation, effective fisheries management, oil exploration, outfitting, research, and other purposes.

An echo sounder is a system that helps to understand underwater conditions and has been used by most naval vessels for many years. The system is one of the simplest applications of sonar (acoustic navigation and ranging) technology, which utilizes the basic principles of acoustics to determine the available water depth.

The theory behind this technology is based on the physics of underwater sound propagation. It works by transmitting acoustic or sound signals or pulses that bounce off obstacles (such as the seabed) and then return, or echo, indicating of the time it took.

Then, from basic principles, using the known speed of sound waves and the time recorded, the water depth can be approximated - the straight-line distance from mean sea level to the seabed. While the term "approximately" was more suitable for earlier versions of the technology, modern echo sounder technology is highly accurate, which significantly reduces the possibility of errors or inaccuracies.

In addition to determining underwater clearance, echo sounders are widely used for purposes such as finding schools of fish and underwater exploration.

How a Sonar Sounder Works and Its Basic Components?

The main components of a sonar sounder are:

1) Transmitter,

2) Transducer,

3) Receiver,

4) Display.

The transmitter generates a short pulse of an alternating current electrical signal through a voltage source directed at the transducer, and the low-power signal is typically converted to a high-power signal through an appropriate power amplifier.

How an Echo Sounder Works?

The transducer in this context is a converter and projector that converts the electrical energy of the signal sent by the transmitter into electrical energy and transmits it underwater.

These sound waves are emitted by the transducer unit, which is mainly located near the bottom of the hull, through the water surface, hit the seafloor, and then bounce back. The transducer captures these reflected sound waves, converts them into electrical energy, amplifies them, and records the resulting signal on the receiver.

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It is important to note that the transducer unit performs two basic functions:

1) The transmitter and receiver units send and receive acoustic signals to and from the vessel (or other related structure).

2) The transducer unit converts the input electrical energy into acoustic or sound wave energy during transmission and converts the acoustic energy of the echo signal into electrical signals during reception.

When the transducer transmits an audio signal, it is usually similar to a projector or speaker unit. When it receives an echo signal, it is similar to a microphone or hydrophone unit.

During transmission, the input is primarily electrical, and the output is acoustic. Conversely, during reception, the input signal is audio or noise, and the output signal along the reverse circuit is an electrical wave.

Some time-based devices record the time from start to finish and are connected to other important components of the echo sounder system to help estimate distance. Additionally, these devices work in conjunction with the transmitter to control the pulse frequency of the signal or waveform generated.

Additionally, for the sound pulse, both when it is transmitted to and from the seabed, various factors may be present, including losses, white noise, and external interference. The amplifier is located within the circuit and is used to increase the amplitude of the electric energy wave, facilitating easier decoding.

Electrical pulse signal

The receiving unit reads various parameters such as amplitude, frequency, duration, etc., from the converted electrical pulse signal and calculates the depth of the seabed using the following simple formula:

Distance (d) = Speed ​​(f) × Time (t) / 2

Where the denominator (2) represents the two-way transmission of underwater sound waves (from the ship to the seabed and back), and t represents the total time required. The calculated data is then displayed on the display unit for use.

In reality, the normal speed of sound waves in water is about 1,500 meters per second. However, this value can vary due to various factors, including weather conditions, sea conditions, extreme salinity, and extreme temperatures. Most modern ships have methods to mitigate these errors and variations, allowing for accurate estimation of water depth.

Traditionally, depth was estimated manually based on the known velocity (v) and the time interval between the transmitted and received signal waves. After that, devices such as echo sounders were integrated into the sounding unit to calculate the data and transmit it to the display unit for reference. Modern technology includes high-speed, user-friendly, integrated digital systems that can perform calculations with great speed and accuracy.

Bridge echo sounding

Echo sounding can be divided into two types:

1) Single beam and

2) Multi-beam.

In simple terms, a single-beam echo sounder transmits a specific beam of acoustic signals covering a small area to determine the depth. Multi-beam echo sounders, on the other hand, are more complex systems that cover a wider area and use complex wave mechanics (such as beam shaping) to better understand the distribution of water depths over a larger area of ​​the seafloor. We will not discuss these systems in detail.

For practical purposes, an echo sounder emits a cone of acoustic signals, which are diverging waves that propagate in a specific area.

An echo sounder must emit short pulses (less than 10 milliseconds), although the value depends on the requirements. It is worth noting that the frequency of the wave signal also depends on the water depth. In deeper waters, lower frequencies are used, ranging from 20 to 25 kHz, while in shallower waters, higher frequencies are employed, such as 300-400 kHz or higher.