11-05-2012, 04:24 PM
Tutorial introduction and historical overview of the need for heading sensors in sonar applications
[attachment=21921]
Historical Overview of Sonar Developments
The development of sonar systems is closely coupled to the evolution of the submarine. By the beginning of the
twentieth century, the threat of a submarine force to commercial and naval shipping was starting to be appreciated.
It is no coincidence that experiments using underwater sound were also taking place at this time. The development
of sonar systems has progressed throughout the twentieth century, with increased activity being occasioned by events
such as two world wars, the cold war and the exploitation of off-shore oil reserves.
The history of the British anti-submarine sonar development is well documented by Hackmann [l] and the majority
of the historical information contained in this paper is taken from this excellent text. A similar review of American
developments is given by Laskey [2]. Urick [3] also provides a brief historical overview of American sonar
developments and an invaluable source of theoretical and experimental results obtained during this period.
The first submarines, as they would be recognized today, were built by John Holland in 1878 and 1881. The navies
of France, America and Russia expressed an interest in these developments. At that time Britain had the largest
navy in the world and perceived no threat from a submarine fleet. This attitude was displayed in the famous
description of submarines by Admiral A.K. Wilson as "underhand, unfair and damned un-English". However, this
attitude rapidly changed with the construction in 1900 of the first British Holland Class submarine built by Vickers
under American guidance. In early 1904 naval exercises were proving just how inhibiting the presence of a small
number of submarines were to the movement of the fleet. Early attempts to detect these submarines were based on
sound tubes coupled to the human ear and hydrophones based on modified microphone inserts from telephone
systems. These experiments would be classified as "passive" (or listening) sonars. It is interesting to note that even
at this early stage the need for directive hydrophones had been appreciated with attempts being made to mount the
active element at the centre of a parabolic reflector. The implication would be that the hydrophone structure
should ideally be connected to some form of direction sensor in order to locate the target.
The Titantic disaster in 1912 resulted in a number of patents being issued for iceberg detection equipment. A
number of attempts were made to detect icebergs using "active" (or transmitting) sonars. These used Fessenden, or
electromechanical sound sources. A field trial in April 1914 resulted in an iceberg being detected at a range of two
miles.
The next major event to have an impact on the development of sonar systems was the declaration of the First World
War in 1914. Germany possessed a fleet of U boats which were initially used as submerged torpedo boats in attacks
against naval vessels. By January 1917 Germany had declared unrestricted war against commerce and this resulted
in the loss of 3.75 million tons of shipping in the first six months. The British navy found itself ill-prepared and
ill-equipped to deal with this threat.
The first attempts to contend with this threat were to introduce shore based passive sonar stations at key points
around the coast. The positions of the omni-directional hydrophones used in these shore stations were surveyed
during installation and thus there was no need for heading sensors to be incorporated into the system. The location
of the submarine was estimated by determining the hydrophone receiving the largest signal amplitude. Simple,
omni-directional dunking hydrophones were also issued in large numbers to the anti-submarine trawler fleet during
1917. These sets were also issued for harbour protection duties for deployment from the side of jetties and wharfs.
These simple sets could only be used when drifting, or a very low speeds, due to the self noise of the vessels. The
first directional hydrophones were fitted to British submarines during 1917 although there is no record of the
beamwidth of these devices having been measured.
The problems of flow noise and vessel self noise encountered in the early passive sonar sets led to a variety of
attempts to tow sonars behind the host vessel.
streamlined wooden body. Problems were encountered with the noise introduced via the tow cable - a problem that
is still with us today ! In 1917 G.H. Nash produced a sophisticated towed body containing an electrically rotatable
hydrophone to determine the direction of a target. Similarly, H.J. Ryan built a towed body which included an
acoustically transparent rubber membrane as part of the structure.
towed 6-9m below the surface and 90-180m behind the host vessel. At a speed of 8 knots a target could be detected
The first British experiments took place in January 1916 with a
This was a 75mm diameter device which was
Acoustics and Sonar Group, University of Birmingham
at a range of 6 km although problems were encountered with entrapped bubbles contained in the wake of the host
vessel. At the same time, the Americans developed the U3 towed sonar tube, or "eel". This was towed at a depth
of 30m and contained 12 hydrophones which were used in two groups of six. These were coupled via electrical
phase shift networks to present a binaural signal to the operator. By deploying two "eels" at different separations
behind the vessel and the use of a hull mounted hydrophone, a primitive passive ranging system was evolved. This
"eel" was probably the first recognisable example of the modem flexible towed array.
It was not until August 1918 that the first examples of active sonars had been fitted to British vessels. The typical
range obtainable with these active devices was of the order of 450m while the best passive sonars were obtaining
ranges of the order of 19km. However, the active sonars operated at higher frequencies (15 - 25 kHz) and could
therefore provide a potential angular resolution of approximately one order-of-magnitude better than the passive
systems as well as providing ranging information.
The inter-war period saw a general improvement in the ability of sonar systems. The major factors influencing the
development of these systems were the availability of thermionic valves and the improving reliability of electronic
components. British and American developments tended to be based on active (asdic) sonar systems whilst the
Germans tended to concentrate on passive sonar systems. At this time, the British scientists and engineers believed
that a submarine could be quietened sufficiently so as to avoid detection by a passive sonar system, thus the only
effective anti-submarine system had to be based on an active or echo location technique. Hull mounted transducers
had become larger in order to provide a greater operating range and an improved angular resolution. At the same
time streamlined dome technology had improved to reduce the effects of flow noise on the transducer.
The advent of the Second World War in 1939 prompted the rapid development and deployment of anti-submarine
sonar systems. By 1942 gyro stabilized transducers were being employed to steer "search-light'' beams of the order
of 15 degrees to a pointing resolution of 2.5 degrees. In 1943 the deep-diving tactics of the German submarine fleet
resulted in the fitting of the Q-attachment to surface ships which had a 3 degree horizontal beamwidth and a 60
degree vertical beamwidth. The Germans were fitting large conformal passive arrays to their capital ships with
similar beamwidths.
In 1940 the Americans started the development of omni-directional and directional sonobuoys. By 1943 these
devices were available for deployment in large quantities. The Germans had developed acoustic homing torpedoes,
wire guided torpedoes and a range of sonar systems for midget submarines and frogmen. By the end of the war, the
typical British passive sonar system could detect a target at a range of 24 km and an active sonar system could detect
a target at a range of 1.2 km.
Post-war developments included the helicopter mounted dunking sonar which was first tested during the 1950's.
The first large aperture, ship-towed, passive arrays (SURTASS) were developed during the 1960's as were
mine-hunting and bottom mapping side-scan sonars, variable depth sonars and ocean floor mounted passive sensors.
By the 1960's the typical passive sonar range had increased to about 160 km and the active sonar range had
increased to about 8 km. During the 1970's and 80's improvements were made by increasing still further the size of
the acoustic arrays and, more spectacularly, by increasing the processing gain with sophisticated digital systems.
However, potential targets have recently become significantly quieter and the passive sonar detection range available
now is probably only a fraction of the value available in the early 1970's. The open literature shows a heightened
interest in active sonar systems and devices with ranges of the order of 160 km are being discussed.
Conclusions about the Historical Development of Sonar Svstems
The majority of techniques that are used in current sonar systems were developed in the early part of this century.
Hull mounted sonars predominated at first and, as these became larger, gyro stabilization and then electronic
stabilization was required to counteract the movement of the vessel. Hull mounted sonars also had the advantage
that the heading reference could be derived from the main heading compass, whether magnetic or gyro, and that the
transducer axes were fixed with respect to the axes of the vessel. The problems introduced by the self noise of the
vessel could only be reduced by mounting the transducers away from the vessel. The first attempts involved towing
the transducer array behind the host vessel. Later developments included bottom mounted sensors, air launched
sensors, dunking sonars, variable depth sonars, diver-held and side-scan sonars. To improve the operational range
and to aid the localization of a target it is essential that the response of all of these devices is directive. This implies
that the performance of the heading sensor is as important as the performance of the sonar itself. For many
applications it is also vital to know other information such as absolute position (sonobuoys), depth (divers and
variable depth sonars) and attitude (side-scan and mapping sonars).
[attachment=21921]
Historical Overview of Sonar Developments
The development of sonar systems is closely coupled to the evolution of the submarine. By the beginning of the
twentieth century, the threat of a submarine force to commercial and naval shipping was starting to be appreciated.
It is no coincidence that experiments using underwater sound were also taking place at this time. The development
of sonar systems has progressed throughout the twentieth century, with increased activity being occasioned by events
such as two world wars, the cold war and the exploitation of off-shore oil reserves.
The history of the British anti-submarine sonar development is well documented by Hackmann [l] and the majority
of the historical information contained in this paper is taken from this excellent text. A similar review of American
developments is given by Laskey [2]. Urick [3] also provides a brief historical overview of American sonar
developments and an invaluable source of theoretical and experimental results obtained during this period.
The first submarines, as they would be recognized today, were built by John Holland in 1878 and 1881. The navies
of France, America and Russia expressed an interest in these developments. At that time Britain had the largest
navy in the world and perceived no threat from a submarine fleet. This attitude was displayed in the famous
description of submarines by Admiral A.K. Wilson as "underhand, unfair and damned un-English". However, this
attitude rapidly changed with the construction in 1900 of the first British Holland Class submarine built by Vickers
under American guidance. In early 1904 naval exercises were proving just how inhibiting the presence of a small
number of submarines were to the movement of the fleet. Early attempts to detect these submarines were based on
sound tubes coupled to the human ear and hydrophones based on modified microphone inserts from telephone
systems. These experiments would be classified as "passive" (or listening) sonars. It is interesting to note that even
at this early stage the need for directive hydrophones had been appreciated with attempts being made to mount the
active element at the centre of a parabolic reflector. The implication would be that the hydrophone structure
should ideally be connected to some form of direction sensor in order to locate the target.
The Titantic disaster in 1912 resulted in a number of patents being issued for iceberg detection equipment. A
number of attempts were made to detect icebergs using "active" (or transmitting) sonars. These used Fessenden, or
electromechanical sound sources. A field trial in April 1914 resulted in an iceberg being detected at a range of two
miles.
The next major event to have an impact on the development of sonar systems was the declaration of the First World
War in 1914. Germany possessed a fleet of U boats which were initially used as submerged torpedo boats in attacks
against naval vessels. By January 1917 Germany had declared unrestricted war against commerce and this resulted
in the loss of 3.75 million tons of shipping in the first six months. The British navy found itself ill-prepared and
ill-equipped to deal with this threat.
The first attempts to contend with this threat were to introduce shore based passive sonar stations at key points
around the coast. The positions of the omni-directional hydrophones used in these shore stations were surveyed
during installation and thus there was no need for heading sensors to be incorporated into the system. The location
of the submarine was estimated by determining the hydrophone receiving the largest signal amplitude. Simple,
omni-directional dunking hydrophones were also issued in large numbers to the anti-submarine trawler fleet during
1917. These sets were also issued for harbour protection duties for deployment from the side of jetties and wharfs.
These simple sets could only be used when drifting, or a very low speeds, due to the self noise of the vessels. The
first directional hydrophones were fitted to British submarines during 1917 although there is no record of the
beamwidth of these devices having been measured.
The problems of flow noise and vessel self noise encountered in the early passive sonar sets led to a variety of
attempts to tow sonars behind the host vessel.
streamlined wooden body. Problems were encountered with the noise introduced via the tow cable - a problem that
is still with us today ! In 1917 G.H. Nash produced a sophisticated towed body containing an electrically rotatable
hydrophone to determine the direction of a target. Similarly, H.J. Ryan built a towed body which included an
acoustically transparent rubber membrane as part of the structure.
towed 6-9m below the surface and 90-180m behind the host vessel. At a speed of 8 knots a target could be detected
The first British experiments took place in January 1916 with a
This was a 75mm diameter device which was
Acoustics and Sonar Group, University of Birmingham
at a range of 6 km although problems were encountered with entrapped bubbles contained in the wake of the host
vessel. At the same time, the Americans developed the U3 towed sonar tube, or "eel". This was towed at a depth
of 30m and contained 12 hydrophones which were used in two groups of six. These were coupled via electrical
phase shift networks to present a binaural signal to the operator. By deploying two "eels" at different separations
behind the vessel and the use of a hull mounted hydrophone, a primitive passive ranging system was evolved. This
"eel" was probably the first recognisable example of the modem flexible towed array.
It was not until August 1918 that the first examples of active sonars had been fitted to British vessels. The typical
range obtainable with these active devices was of the order of 450m while the best passive sonars were obtaining
ranges of the order of 19km. However, the active sonars operated at higher frequencies (15 - 25 kHz) and could
therefore provide a potential angular resolution of approximately one order-of-magnitude better than the passive
systems as well as providing ranging information.
The inter-war period saw a general improvement in the ability of sonar systems. The major factors influencing the
development of these systems were the availability of thermionic valves and the improving reliability of electronic
components. British and American developments tended to be based on active (asdic) sonar systems whilst the
Germans tended to concentrate on passive sonar systems. At this time, the British scientists and engineers believed
that a submarine could be quietened sufficiently so as to avoid detection by a passive sonar system, thus the only
effective anti-submarine system had to be based on an active or echo location technique. Hull mounted transducers
had become larger in order to provide a greater operating range and an improved angular resolution. At the same
time streamlined dome technology had improved to reduce the effects of flow noise on the transducer.
The advent of the Second World War in 1939 prompted the rapid development and deployment of anti-submarine
sonar systems. By 1942 gyro stabilized transducers were being employed to steer "search-light'' beams of the order
of 15 degrees to a pointing resolution of 2.5 degrees. In 1943 the deep-diving tactics of the German submarine fleet
resulted in the fitting of the Q-attachment to surface ships which had a 3 degree horizontal beamwidth and a 60
degree vertical beamwidth. The Germans were fitting large conformal passive arrays to their capital ships with
similar beamwidths.
In 1940 the Americans started the development of omni-directional and directional sonobuoys. By 1943 these
devices were available for deployment in large quantities. The Germans had developed acoustic homing torpedoes,
wire guided torpedoes and a range of sonar systems for midget submarines and frogmen. By the end of the war, the
typical British passive sonar system could detect a target at a range of 24 km and an active sonar system could detect
a target at a range of 1.2 km.
Post-war developments included the helicopter mounted dunking sonar which was first tested during the 1950's.
The first large aperture, ship-towed, passive arrays (SURTASS) were developed during the 1960's as were
mine-hunting and bottom mapping side-scan sonars, variable depth sonars and ocean floor mounted passive sensors.
By the 1960's the typical passive sonar range had increased to about 160 km and the active sonar range had
increased to about 8 km. During the 1970's and 80's improvements were made by increasing still further the size of
the acoustic arrays and, more spectacularly, by increasing the processing gain with sophisticated digital systems.
However, potential targets have recently become significantly quieter and the passive sonar detection range available
now is probably only a fraction of the value available in the early 1970's. The open literature shows a heightened
interest in active sonar systems and devices with ranges of the order of 160 km are being discussed.
Conclusions about the Historical Development of Sonar Svstems
The majority of techniques that are used in current sonar systems were developed in the early part of this century.
Hull mounted sonars predominated at first and, as these became larger, gyro stabilization and then electronic
stabilization was required to counteract the movement of the vessel. Hull mounted sonars also had the advantage
that the heading reference could be derived from the main heading compass, whether magnetic or gyro, and that the
transducer axes were fixed with respect to the axes of the vessel. The problems introduced by the self noise of the
vessel could only be reduced by mounting the transducers away from the vessel. The first attempts involved towing
the transducer array behind the host vessel. Later developments included bottom mounted sensors, air launched
sensors, dunking sonars, variable depth sonars, diver-held and side-scan sonars. To improve the operational range
and to aid the localization of a target it is essential that the response of all of these devices is directive. This implies
that the performance of the heading sensor is as important as the performance of the sonar itself. For many
applications it is also vital to know other information such as absolute position (sonobuoys), depth (divers and
variable depth sonars) and attitude (side-scan and mapping sonars).