50 Fun Facts About Sonar

What does the acronym SONAR stand for?

The study of underwater sound itself is called hydroacoustics.

Which kind of sonar emits pulses of sound and listens for the echoes?

Passive sonar gives away nothing, which is why submarines rely on it most of the time.

Who is recorded as first using a tube in the water to detect ships by ear, in 1490?

Underwater bells were later hung near lighthouses in the 19th century to warn ships of hazards.

Which 1912 disaster prompted the first patent for an underwater echo-ranging device?

Richardson was a meteorologist; a German, Alexander Behm, patented an echo sounder the following year.

Which Canadian engineer detected an iceberg by echo ranging off Newfoundland in 1914?

His oscillator worked at about 500 Hz and could give range but not bearing.

Which French physicist worked with Constantin Chilowsky on detecting submarines in 1915?

Langevin drew on the piezoelectric effect discovered by Pierre Curie, using thin quartz crystals.

Which crystal did the first practical British echo-ranging apparatus use in 1917?

Secrecy was so tight that the word quartz was replaced in paperwork by ASDivite.

What did the ASD in the British sonar name ASDIC actually stand for?

In 1939 the Admiralty told the Oxford English Dictionary it meant Allied Submarine Detection Investigation Committee, a story still widely repeated though no such committee existed.

Which Harvard acoustics professor coined the term SONAR as an equivalent to RADAR?

Hunt received the Medal for Merit from President Truman in 1947 for his wartime work.

What is the pulse of sound emitted by an echo-ranging sonar commonly called?

The round-trip time, scaled by the speed of sound and halved, gives the range.

Roughly how fast does sound travel in seawater?

That is more than four times faster than sound moves in air.

Who showed on Lake Geneva in 1841 that sound is over four times faster in water than air?

Colladon also campaigned to light Geneva with gas lamps, achieved on Christmas Day 1844.

What is the ocean temperature layer, 30 to 100 metres down, that bends sound?

American engineers discovered thermoclines and their effect on sound in the 1930s.

Which law describes how sound refracts as it crosses layers of different sound speed?

Higher pressure raises sound speed, so deep sound bends away from the high-speed region.

Which sailors' term describes sonar with the transmitter and receiver in the same place?

When they are separated, it is bistatic; most sonars use one array for both jobs.

Which anti-submarine weapon problem did the Hedgehog and Squid solve?

Depth charges had to be dropped over the stern, so the hunter went blind at the crucial moment.

Which Royal Navy officer developed the two-ship 'creeping attack' using ASDIC?

One ship tracked the U-boat while a second, sonar off and at five knots, made the attack on its instructions.

Under what codename did the British develop the first sonobuoys in 1944?

Britain had handed its ASDIC technology to the United States for free in September 1940.

What is a sonobuoy?

A float with a radio transmitter stays on the surface while hydrophones sink to a chosen depth.

Which crystal made Rochelle salt obsolete in US transducers within nine wartime months?

Lead zirconate titanate (PZT) later became the standard piezoelectric material.

Which US Navy sonar used a large array of 432 individual transducers for decades?

Its early transducers failed so often that the Navy switched to sealed, non-repairable modules.

Why does a towed array sonar trail its hydrophones far behind the vessel?

It also covers the baffles, the blind spot directly astern of a hull-mounted sonar.

What is a hydrophone?

Most contain a piezoelectric transducer that produces a voltage when a sound wave squeezes it.

Which sound-emitting organ makes a fish visible to sonar?

Commercial fishing fleets now rely almost completely on sonar and sounders to find fish.

Which type sweeps fan-shaped pulses sideways to image the seafloor and find wrecks?

Marine archaeologists, shipwreck hunters and mine hunters all use it.

Which Tudor flagship did Harold Edgerton help locate in 1967 with Martin Klein's sonar?

Klein's team had built the first successful towed commercial side-scan system between 1963 and 1966.

What does a multibeam echosounder produce from a single ping?

The US Navy's SASS system of the early 1960s pioneered swath mapping for its submarines.

Which method of measuring depth did echo sounding replace?

One of the first commercial units, the Fessenden Fathometer, went aboard the liner SS Berkshire in 1924.

Which German inventor was granted a patent for echo sounding in July 1913?

Like Richardson's British patent, it came in the wake of the Titanic sinking.

What is the SOFAR channel?

Sound trapped in it can travel enormous distances; Ewing and Worzel heard charges set off 900 nautical miles away in 1944.

What was SOSUS?

An array ending at Barbados made the first detection of a Soviet nuclear submarine entering the Atlantic on 6 July 1962.

Which cetaceans most often strand after exposure to mid-frequency naval sonar?

In the Canary Islands, mass strandings stopped after naval exercises with sonar were banned.

Which zoologist coined the term echolocation and first demonstrated it in bats?

Lazzaro Spallanzani had shown in the 18th century that bats fly by some sense besides vision, without identifying hearing.

Which Swiss naturalist concluded in 1798 that hunting bats rely on hearing?

Walter Louis Hahn confirmed the findings in 1908, decades before the word echolocation existed.

Roughly how many clicks per second can a bottlenose dolphin's hearing resolve?

Varying click rates produce the familiar barks, squeals and growls of dolphins.

Which sound made by fast propellers gives away a vessel to passive sonar?

Submarines run slowly and quietly precisely to avoid producing it.

Which phenomenon lets a single-frequency sonar measure a target's radial speed?

Allowance must be made for the searching platform's own motion, since that shifts the echo too.

What is sodar?

Acoustic location in air was also used to detect aircraft before radar arrived.

Which country's H-class submarines carried Fessenden oscillators in 1915?

The oscillator doubled as an underwater telegraph, tapping out Morse code through the water.

Which German torpedo of March 1943 was among the first passive acoustic homing torpedoes?

It was soon replaced by the T5 Zaunkönig, which the Allies countered with noisemaking decoys.

Why do submarines rely on sonar more than surface ships do?

A submarine's nose-mounted array, hull arrays and towed array together cover a full circle.

Which Royal Navy ship tested ASDIC in 1920, before production began in 1922?

An anti-submarine school named HMS Osprey followed at Portland in 1924.

Which Royal Navy frigates were first fitted with the Thales Sonar 2087 towed array in the 2000s?

It is a low-frequency active sonar with both active and passive arrays, fitted to Type 23 frigates from 2006 and planned for their Type 26 successors.

Which material became typical for sonar domes, replacing older steel designs?

The SQS-26 dome was about the size of a 60-foot boat, an upper limit for hull sonars.

Which Canadian physicist led Britain's active sound detection project from 1916, producing a prototype in 1917?

His work for the Anti-Submarine Division gave the British ASDIC system its name.

The hand-held LIMIS imaging sonar was designed to help patrol divers find what?

It works in low-visibility water and can also be mounted on a remotely operated vehicle.

In the late 19th century, underwater bells were used alongside lighthouses and lightships to do what?

Echo-location in water only took off after the Titanic disaster prompted the first patents in 1912.

The Cold War SOSUS hydrophone network was developed and installed with which American company?

Bell Laboratories handled research and Western Electric the manufacturing.

What name is given to a system designed to detect and locate the pings of hostile active sets?

Submarines rarely go active themselves, since a ping gives away the operator's presence and position.

In passive listening, the process of working out a contact's trajectory is called what?

The resulting 'solution' gives the target's course and speed; unique engine sounds feed acoustic intelligence, or ACINT.