MPA Logo, San Francisco Maritime National Park Association, USS Pampanito, Historic Ships at Hyde Street Pier, Education Programs Maritime Park Association Home Page Maritime Park Association Home Page Events Maritime Park Association Home Page Maritime Park Association Home Page Maritime Park Association Home Page Volunteer Membership Donate Maritime Park Association Home Page USS Pampanito Submarine Historic Ships at Hyde Street Pier Education Programs About Maritime Park Association Home Page Directions to Maritime Jobs at Maritime Facility Rental at Maritime Trustees of the Association Calendar Press Room Store Maritime Map
APPENDIX

DEFINITIONS OF FIRE CONTROL TERMS AND SYMBOLS

AS APPLIED TO SONAR

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.

  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

 
323

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

  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.

 
324

Previous Chapter
Previous Chapter
Sonar Home Page
Sonar Home Page
Next Chapter
Next Chapter

 

Copyright © 2013, Maritime Park Association.
All Rights Reserved.
Legal Notices and Privacy Policy
Version 3.00