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HISTORY OF

SON

The use of sound to ‘echo locate’ underwater, in the same way that bats use sound for aerial navigation, seems to have been prompted by the Titanic disaster of 1912. The world’s first patent for an underwater echo ranging device was filed at the British Patent Office by English meteorologist Lewis Richardson a month after the sinking of the Titanic, and a German physicist Aleander Behm obtained a patent for an echo sounder in 1913.


NAR

WHAT IS

Sonar, short for Sound Navigation and Ranging, is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves.

To the left, this image illustrates how a ship utilizes the reflecting properties of sound waves to determine the depth of the ocean. A sound wave is transmitted and bounces off the sea be. Because the speed of sound is known and the time lapse between sending and recieving the sound can be measured, the distance from the bottom of the ocean can be measured.


HOW DOES SONAR WORK? HOW DOES SONAR WORK? HOW DOES SONAR WORK? HOW DOES SONAR WORK WORK?


Sonar uses sound waves to ‘see’ in the water.

The vessel sends out rapid sound pulses that bounce off the sea floor and back to scan what’s below. These surroundings produce amazingly detailed echo sounders, shown here measuring the depth of the sea floor. Multibeam surroundings create nautical charts and produce colour maps of the underwater terrain. In general, red is ussed to show shallow depts in the ocea, and blue or purple illustrates greater depth.


ACTIVE SONAR Active Sonar is helpful for exploring and mapping the ocean because sound waves travel farther in the water than do radar and light waves. Researchers and scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the sea floor such as shipwrecks, and map the sea floor itself. Scientists have recently begun using Active Sonar to identify and monitor many different species of marine life by exploring the way the sound waves travel through fish’s gall bladders. Active Sonar is also used in the military to locate, identify and even communicate with enemy and ally vessels through pulses or chirps.


Active sonar uses a sound transmitter and a receiver. This process creates a pulse of sound, often called a “ping”, and then listens for reflections (echo) of the pulse. This pulse of sound is generally created electronically using a sonar projector consisting of a signal generator, power amplifier and electro-acoustic transducer/array. To measure the distance to an object, the time from transmission of a pulse to reception is measured and converted into a range by knowing the speed of sound.

THE SPEED OF SOUND UNDERWATER IS 1500m/s DISTANCE = SPEED / TIME HOWEVER, THE SIGNAL HAS TRAVELLED TO THE OBJECT AND BACK, SO MUST BE HALVED TO FIND THE DISTANCE. THEREFORE: DISTANCE = (1500 x TIME)/2


Passive Sonar involves silently listening to underwater soundwaves and signals emitted by other sources, such as submarines, vessels and marine life, to locate them. Passive sonar systems can be arrays of hydrophones towed behind a ship or submarine or cabled to shore. A hydrophone is a microphone designed to be used to listen to or record sound underwater. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change. When used in a line formation, these arrays will detect sound from their desired direction whilst subtracting signals from other directions. Passive Sonar has historically been used for military purposes, such as in submarine combat, but modern environmental concerns mean this method is being used increasingly to monitor marine life, such as whales.

PASSIVE


HYDROPHONE ARRAY

SONAR


SEARCHLIGHT

SONAR

Searchlight sonar works by transmitting a single ultrasonic beam that is 6 degrees wide. The sonar will then rotate a further 6 degrees and repeat the process. In this way, searchlight sonar can search a wide area sequentially. High frequency ultrasonic waves take a comparatively long time travelling through water and this can limit the search speed. Due to the narrow beam transmitted, somtimes the sonar will not display the surroundings properly while the boat is in motion. 6de

gre

es

wid

e

6degrees wide

Searchlight sonar is used to get information from the water below in 360 degrees around the ship. The transducer rotates and the beam angle can be changed freely to make sure that any fish schools and reefs close by are found. Searchlights sonar is name after how its operation is simillar to a search light.

fish

ship


SCANNING

SONAR

Scanning sonar can search 360 degrees around the vessel in an instant. Due to the wide beam, no dead zones (zones that will not be properly displayed due to narrow beam width) will appear in the horizontal direction. Since the scanning sonar searches 360 degrees around the ship, the same fish school can be identified multiple times. Based on the information recieved by the sonar it is also possible to estimate where the fish school is heading and at what speed.

Unline a searchlight sonar that rotates in 6 degree steps at a time, a scanning sonar sequentially turns on its oscilators in an instant, giving a full 360 degree view. Scanning sonars are especially useful when searching for fish such as tuna, since they can swim at very high speeds. ship


CHIRP SONAR

CHIRP (Compressed High-Intensity Radiated Pulse) is a modern method of Sonar which has recently become availableto the public to aid with fishing. Hand held products are available for inland fishing and coastal fishing and larger so-called ‘black boxes’ are available for fishing at greater depths.

Instead of sending a single frequency, CHIRP sonar sends a continuous sweep of frequencies ranging from low to high. The technology then interprets frequencies individually upon their return. Since this continuous sweep of frequencies provides CHIRP with a much wider range of information, it is able to create a much clearer, higher resolution image, as shown above.


STANDARD SONAR VS CHRIP SONAR


WHALES Toothed whales and dolphins use sonar to navigate and communicate underwater. Much the same as submarines, this is because sound travels more efficiently and effectlively underwater than light. This helped them to locate food, predators and other members of their species. They communicate with each other through low frequency clicks humans are unable to hear.


BATS Bats use sonar to navigate and forage, often in total darkness. They generate ultrasound via the larynx and emit the sound through the open mouth or the nose, and listen for the echo with their ears - allowing them to detect prey, predators and obstacles in their path.


JINGLEI SHEN & LOUISE MARSHALL

How Does Sonar Work?  

Louise Marshall & Jinglei Shen

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