DUAL SINGLE-AXIS SYSTEM -This term refers to a
system of gimbaling employed to position two planes
in space each of which rotates about a single axis of rotation. In a typical sonar system one of the planes is a
sound plane, perpendicular to the deck, used to determine
the bearing of the sonar target. The other is a sound
plane, parallel to the deck, used to determine the depression of the sonar target. A dual single-axis system is
shown in figure 9-8.
LINE OF SIGHT -The line of sight as used in this text
refers to a straight line from the point of origin to its
termination.
LINE OF SOUND -The line of sound as used in this text
refers to a line extending from the sound head along the
sound-beam path (figure 9-10) or along the line of intersect ion of two single-axis sound planes (figure 9-12). It
deviates from a straight line by the amount the sound
beam is refracted by temperature, salinity, and pressure
gradients present in the water medium through which the
sound travels.
SONAR DECK PLANE -AS used in this text, the sonar
deck plane is the plane through the center of the depth-determining-equipment transducer and parallel to the
reference surface of the stable element.
SONAR HORIZONTAL PLANE -AS used in this text, the
sonar horizontal plane lies on the horizontal plane through
the center of the depth-determining-equipment transducer.
SOUND BEAM -This term is used to designate the pattern formed by lines of sound emitted from a sound head
mounted on three mutually perpendicular axes.
SOUND HEAD -The term "sound head" is used to
designate the sonar transducer or hydrophone including
its housing and mounting.
SOUND PLANE -The term "sound plane" is used to
designate the pattern formed by the sound emitted from
a sound head mounted on a single axis of rotation.
THREE-AXIS SYSTEM -This term refers to a system
of gimbaling employed to position a line in space about
three axes of rotation relative to the deck of the ship.
These axes are a train axis perpendicular to the deck, a
crosslevel axis parallel to the deck, and a level axis, in the
horizontal plane perpendicular to the crosslevel axis. The
line positioned may be a line of sight, the axis of a sound
beam, or any other line. A three-axis system is shown
in figure 9-10.
TRANSDUCER -The transducer is the sensitive receiving
and transmitting element of a sound head.
* * * *
Bq-TRUE SONAR TARGET BEARING -The angle between a north-and-south vertical plane and the vertical
plane through the line of sight to the sonar target, measured in a horizontal plane clockwise from the north.
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Br-RELATIVE TARGET BEARING -The angle between
the vertical plane through the fore-and-aft axis of own
ship and the vertical plane through the line of sight from
the main director, measured in a horizontal plane clockwise from the bow.
B'r-STABLE ELEMENT TRAIN -The angle between the
fore-and-aft axis of own ship and the vertical plane
through the line of sight from the main director to the
target for which the stable element is trained, measured
in the deck plane clockwise from the bow.
Brq-RELATIVE SONAR TARGET BEARING -The angle
between the vertical plane through the fore-and-aft axis
of own ship and the vertical plane through the line of sight
to the sonar target, measured in a horizontal plane clockwise from the bow.
B'rq-STABILIZED SONAR TRAIN -The angle between
the fore-and-aft axis of own ship and the vertical plane
through the axis of the sound beam at the sound head
measured in the deck plane clockwise from the bow. The
stabilized sonar train is normally used in referring to three-axis systems.
B'r'q-AZIMUTH SONAR TRAIN -The angle between
the fore-and-aft axis of own ship and the plane perpendicular to the deck through the line of sight to the sonar target.
measured in the sonar deck plane clockwise from the bow.
Co-OWN SHIP'S COURSE -The angle between the
north-and-south vertical plane and the vertical plane
through the fore-and-aft axis of own ship, measured in a
horizontal plane clockwise from the north. This angle is
normally measured by the gyrocompass.
Eq-APPARENT DEPRESSION ANGLE -The angle of depression below the sonar horizontal plane of the acoustic
path of the QDA transducer to the sonar target, measured
in the vertical plane through the line of sight to the sonar
target.
Eq differs from Etq by the effect of refraction because
of variations in velocity in the water caused by temperature
salinity, and pressure gradients. For "on target" indications
cEtq ± jEtq = Eq.
ΔEq-INCREMENT OF SONAR DEPRESSION -Changes in
apparent depression angle (Eq).
E'q'-SONAR ACOUSTIC DEPRESSION FROM DECK -The
angle between the direction, at the QDA transducer, of the
acoustic path to the sonar target and the sonar deck plane,
measured in a plane through the line of sight to the sonar
target and perpendicular to the sonar deck plane.
Eqr-REFRACTED DEPRESSION ANQLE -The actual depression angle of the sound beam after passing through the
thermocline.
E'q's-"ON TARGET" DEPRESSION OF DEPTH-DETERMINING-EQUIPMENT TRANSDUCER BEAM -The angle of the
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beam of the depth-determining-equipment transducer from
the sonar deck plane, measured in the plane through the
fore-and-aft axis of own ship and perpendicular to the
deck, when an "on target" indication is obtained. This
angle is the tilt of the transducer.
Etq-SONAR TARGET DEPRESSION -The angle of depression below the sonar horizontal plane of the line of
sight to the sonar target, measured in a vertical plane
through the line of sight to the sonar target.
cEtq-COMPUTED SONAR TARGET DEPRESSION -The
predicted sonar target depression (Etq), determined by the
OKA-1 equipment from the velocity of sound in the water,
the latest indications of the depth of the thermocline and
sound range (Rq), and the target depth below transducer
(H'q)i
This computed angle is used to assist the depth-determining-equipment operator to follow the sonar target
with the acoustic beam.
jEtq-ADJUSTMENT OF COMPUTED SONAR TARGET DEPRESSION -The adjustment of the computed sonar target
depression (cEtq) by the depth-determining-equipment
operator to correct for deviations of the acoustic beam off
the target as indicated by the depth-deviation indicator.
Hq-SONAR TARGET DEPTH -The vertical depth of
the sonar target below the surface of the water.
Hg-RELATIVE TARGET DEPTH -The depth of the
target relative to the depth of the depth-determining-equipment transducer.
L-LEVEL ANGLE -Measured about an axis in the
horizontal plane; it is the angle (figure 9-6) between the
horizontal plane and the deck plane, measured in the
vertical plane through the line of sight. This angle is
positive when the deck toward the target is below the
horizontal plane. The level angle is shown in figure 9-6.
Lq-SONAR LEVEL ANGLE -Measured about an axis
in the horizontal plane; it is the angle between the horizontal plane and the deck plane measured in a vertical
plane through the axis of the sound beam at the sound
head. This angle is positive when the deck toward the
target is below the horizontal plane. The sonar level
angle is shown in figure 9-9.
M-ROLL -Measured about an axis in the deck; it is
the angle measured in the athwartship plane perpendicular
to the deck between its intersection with the horizontal
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plane and the deck plane. The roll is positive when the
starboard side of the ship is up. The angle of roll is shown
in figure 9-6.
N-PITCH -Measured about a horizontal axis; it is the
angle measured about the intersection of the horizontal
plane with the athwartship plane perpendicular to the
deck, between the vertical plane and a plane perpendicular
to the deck through this axis. This pitch is positive when
the bow of the ship is up. The angle of pitch is shown in
figure 9-6.
PVq-DEPTH OF DDE TRANSDUCER -Depth of the
transducer below the surface of the water.
Rq-SOUND RANGE -The distance from the center
of the azimuth transducer to the sonar target, measured
along the sound path.
Rhq-HORIZONTAL SOUND RANGE -The projection of
the sound range (Rq) on a horizontal plane.
dRhq-HORIZONTAL SOUND RANGE RATE -The time
rate of change of horizontal sound range (Rhq).
V or v-VELOCITY OF SOUND IN MIXED LAYER -The
velocity of sound in the layer of water near the surface of
the ocean.
ΔV-VELOCITY DECREASE THROUGH THE THERMOCLINE -The decrease in the velocity of sound in passing
through the thermocline.
VZ-VERTICAL COMPONENT OF THE VELOCITY OF
SOUND-The speed at which a sound beam travels downward.
Zd-CROSSLEVEL ANGLE -Measured about an axis in
the deck; it is the angle (figure 9-6) that is measured about
the intersection of the plane of the deck with the vertical
plane through the line of sight for which the stable element
is trained, between the vertical plane and a plane perpendicular to the deck through this axis. This angle is
positive if, when facing the target, the deck on the observer's right is up. The crosslevel angle is shown in
figure 9-6.
Zdq-SONAR CROSSLEVEL ANGLE -Measured about an
axis in the deck ; it is the angle which is measured about the
intersection of the plane of the deck with the vertical plane
through the axis of the sound beam at the sound head,
between the vertical plane and a plane perpendicular to
the deck through this axis. This angle is positive if,
when facing the target, the deck on the observer's right
is up.
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