Sonar - SOund, NAvigation and Ranging
The word Sonar is an American term first used in World War
II, it is an acronym for SOund, NAvigation and Ranging. The British also call
Sonar, ASDICS, which stands for Anti-Submarine Detection Investigation
Committee. Later developments of Sonar included the echo sounder, or depth
detector, rapid-scanning Sonar, side-scan Sonar, and WPESS
(within-pulseectronic-sector-scanning) Sonar.
United States
submarines began using sonar toward the end of WW2 to navigate through Japanese
minefields. Ned Beach, upon taking command of USS Piper (SS-409), had his first
war patrol as skipper of that boat delayed while a sonar device for detecting
and avoiding underwater mines was being installed. As a result, he and his
submarine only reached Japanese waters, after negotiating through an underwater
minefield submerged, just as the war ended.
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Radio Operations Aboard US Submarines
By Robert E. Straub
QC/JK SONAR:
Submarines were equipped with both active and passive sonar gear. The QC/JK
gear was located in the Conning Tower. These were companion units with the QC
gear being the active and passive sonar and the JK gear was the passive sonar
only. Both sonars were manned when the submarine was submerged. A large bearing
indicator, for both the QC and JK sonars, indicated the relative position to
the submarine's bow of the sound head bearing. The QC sonar had the
"pinging" capability, but was rarely, if ever, used due to
compromising the submarine's position. The sound heads were raised. lowered and
trained from the operating positions in the Conning Tower. The raising and
lowering was done by a hydraulic system and the training was done by an
electric motor controlled by a handle at the operating station for both the QC
and JK sonars. The lowering and raising mechanism for the two sound heads was
located at the after end of the forward torpedo room. This allowed the sound
heads to be raised inside a protective well when the submarine was on the
surface.
The
QC sonar was equipped with a straight key and CW could be used for emergency or
identifying purposes.
Normally headphones were worn by the sonar operators. However, speakers were
available.
FATHOMETER:
The Fathometer, located in the Control Room, was used to measure the depth of
the water from the submarine's keel to the ocean floor. A "ping"
would be sent out and the time delay in receiving the return echo would
establish the depth of the water. Again, for security and safety purposes this
was rarely used. I know of only one occasion that a single "ping" was
used for measuring the depth of the water.
JP SONAR;
The JP Sonar gear, passive only, was located in the Forward Torpedo Room and
its associated hydrophone was located directly overhead on the main deck. The
hydrophone was coupled to the unit by means of a shaft, gear and a crank
handle.
Rotation
of the hydrophone was strictly by man power. With the hydrophone being located
topside it allowed the submarine to "hear" when sitting on the ocean
floor.
The
sonar operators were trained to fire a special acoustic torpedo with this JP
gear.
Late during WWII the JP sonar was replaced with the JT version. This used a
larger hydrophone and the training mechanism was improved from the manual
operation to a electrical/hydraulic system.
NOTE: I'm not sure of the designers of this sonar equipment, but I do believe
that it was the Underwater Lab at New London, which I also believe has changed
its name.
#
In World War II, the
Americans used the term SONAR for their systems, coined as the
equivalent of RADAR. RADAR was considered very glamorous and effective, and
they wanted to cash in on the name. To be literal they should have named it
SODAR (Sound Detection and Ranging) to be the equivalent of, standardization of
signals led to the dropping of ASDIC in favor of SONAR for all
NATO countries.
There are two major kinds of sonar, active and passive.
Active sonar creates
a pulse of sound, often called a "ping", and then listens for
reflections of the pulse. The pulse may be at constant frequency or a chirp of
changing frequency. If a chirp, the receiver correlates the frequency of the
reflections to the known chirp. The resultant processing gain allows the
receiver to derive the same information as if a much shorter pulse of the same
total power were emitted. In general, long-distance active sonars use lower
frequencies. The lowest have a bass "BAH-WONG" sound. To measure the
distance to an object, one measures the time from emission of a pulse to reception.
Passive sonars
listen without transmitting. They are usually military (although a few are
scientific). Passive sonar systems usually have large sonic databases. A
computer system frequently uses these databases to identify classes of ships,
actions (i.e. the speed of a ship, or the type of weapon released), and even
particular ships.
Definitions relating to sound and sonar gear
Absorption. The loss of energy by a sound wave when it
strikes an obstacle which does not reflect it completely.
Alternating current
(A C). Electric current
which flows first in one direction and then in the other.
Amplifier. A device which builds up a weak electric
current into a stronger one.
Amplitude. The maximum extent of a vibrating movement.
With sound, the greater the amplitude, the louder the sound.
Attenuation. The weakening of a sound wave as it
travels, caused by losses due to friction, absorption, and scattering.
Audio frequency. Another-term for sonic frequency; that is,
below 15,000 cycles per second. Compare Radio frequency.
Audio-frequency-amplifier. An amplifier for use with alternating
currents of frequencies less than 15,000 cycles per second.
Background noise. Noise that tends to mask the sounds you
want to hear. Chiefly water noise and noise from the receiver itself.
Band filter. An audio filter which suppresses all
frequencies except those between a given high and low limit. For example, the
band filter on the WCA gear suppresses all frequencies below 600 cycles and
above 1,000 cycles.
Beam. A cone of sound waves, such as is used in
echo-ranging. Normally, a beam can be obtained only by using supersonic
frequencies.
Beat frequency. The frequency obtained by mixing two
different frequencies. For example, by mixing 60,800 and 60,000 cycles, we
obtain a beat frequency equal to their difference of 800 cycles. This is called
heterodyning.
Cavitation. The formation of a series of vacuums when
propellers are turning so rapidly that the water does not flow in immediately
as the blade passes through. Propeller noise is greatly increased when
cavitation occurs.
Compression. The part of a sound wave where the
particles are packed together more closely than normal.
Cycle. A complete sound wave
compression-plus-rarefaction.
Decibel. A unit of measurement of intensity of
sounds.
Detector. Generally, anything that enables sound to
be heard; e.g. the ear. Specifically, in the receiver-amplifier, the detector
mixes two supersonic frequencies to give a frequency that can be heard. Also
called a "mixer."
Diffraction. The tendency of sound waves to bend around
an obstacle in their path and meet somewhere beyond. This accounts for your
being able to hear sounds around a corner. (Do not confuse with
"refraction.")
Direct current
(DC). Electric current that
flows continuously in the same direction. A storage battery gives direct
current.
Driver. An electrical device used to send a burst
of supersonic sound (ping) into the water by means of the projector. In the WCA
gear, there are a QB and a QC driver.
Frequency. Number of cycles per second.
Gyrocompass
repeater. A device which
repeats the movement of the master gyrocompass. The inner dial on the bearing
indicator is a gyrocompass repeater dial. The main gyrocompass on a submarine
is in the control room.
Heterodyning. The mixing of two frequencies to obtain the
beat frequency, which is the difference between them.
Homogeneous water. Water in which the temperature does not
change with depth.
Hydrophone. Any device for picking up sound waves from
water. It is called a projector only when it also sends sounds out into the
water.
Intermediate
frequency (IF). The
frequency into which the energy entering the superheterodyne receiver is
converted in the intermediate stage. In WCA gear, this is 60 kilocycles.
Isothermal. Uniform in temperature. Homogeneous water
is isothermal.
Kilocycle (kc). One thousand cycles.
Magnetostriction. Change in size of a metal tube when
subjected to an electric current. This principle is used in the JP hydrophone
and in the QC and NM projectors.
Modulator. A device which causes a sound to change in
pitch continuously. Sometimes used by surface ships in echo-ranging, when an
echo is difficult to distinguish.
Negative thermal
gradient. Decrease in
temperature of water with depth.
Noise level. The volume of background noise heard in the
headphones or on the loudspeaker.
Oscillator. A device that produces an alternating
current at a particular frequency.
Piezoelectric
effect. The development of
an electric current when a Rochelle salt crystal changes in size. This
principle is used in JK and QB projectors. Compare Magnetostriction.
Positive thermal
gradient. Increase in
temperature of water with depth.
Projector. The hydrophone portion of QC, QB, and NM
gear. Although called a "projector," in submarines it is principally
used to pick up sounds. In echo-ranging, it projects the ping into the water.
Quick beating. Bearing of the maximum loudness in sweeping
across the target. Also called "Maximum bearing."
Radio frequency. Frequency above 15,000 cycles per second,
Compare Audio frequency. Radio-frequency amplifier. An amplifier for use with
alternating currents of frequencies higher than 15,000 per second.
Range rate. The rate in knots at which a target's range
is changing. Useful in determining the speed of the target.
Rarefaction. The part of a sound wave where the
particles are thinned out to less than normal density.
Resonance. The tendency of an object or an electrical
circuit to respond well to a particular frequency, but poorly to other
frequencies.
Reverberations. The multiple echoes reflected from the
surface, bottom, and many small irregularities in the water. In echo ranging,
distinguished from the echo, which comes from the target.
Salinity. The saltiness of water. Normal salinity of
sea water is 35 parts of salt per thousand.
Scattering. The loss of energy by a sound wave caused
by its striking such irregularities in the water as seaweed, fish, and en
trapped air bubbles.
Screen. The antisubmarine escort craft which are
protecting a convoy.
Sonic frequencies. Frequencies less than 15,000 cycles per
second.
Sound shadow. The region beyond an obstruction where a
sound is not heard. See Diffraction.
Split bearing. A bearing obtained by computing the middle
point between where the signal comes in and where it goes out in sweeping
across the target. Split bearings are used only when quick bearing cannot be
obtained.
Sweeping. Turning the projector or hydrophone so that
it goes through the entire arc of the target's propeller sounds.
TDC. The Torpedo Data Computer-a device in the
conning tower which figures out the correct firing data, using the facts of
bearings, ranges, course, and speed.
Transducer. The technical term for what is generally
called a "projector." A transducer operates both as a hydrophone
(picking up sound vibrations and converting them into electric current pulses)
- and as a projector (transforming electric current pulses into sound
vibrations and projecting them into the water).
Vibration. A continuous back - and - forth movement,
producing sound waves in the medium.
Wake. The ribbon of churned-up water astern of a
moving ship or submarine. It consists of small currents, eddies and entrapped
air bubbles.
Wave length. The distance from a given point on one
compression to the corresponding point of the next compression of a sound wave.
The Fleet Type Submarine Online
Submarine Sonar Operator's Manual
Submarine Sonar Operator's Manual