INTRODUCTION TO SONAR 



and missiles. Volume 1 contains the nomenclature 

 for the quantities applicable to solutions of the 

 gun fire control problem. Volume 2 covers the 

 nomenclature for underwater related quantities. 

 Volume 3 has the standai'd nomenclature for 

 mrssile related quantities. 



The plan of the OP 1700 system follows 

 the general pattern of the previous system, with 

 modification to permit introduction of new quan- 

 tities. It has greater flexibility and wider appli- 

 cation to advanced fire control problems. 



In some instances, quantities in the new 

 system have different symbols than they do in 

 the old system. True target bearing, for example, 

 uses the capital letter B in the old system, but 

 in the new system it is symbolized as By. Target 

 course in the old system is represented by Ct, 

 whereas in the new system the modifying letter 

 t is omitted. 



The geometrical quantities used in naval fire 

 control are those quantities involved in the 

 mathematical solution of the general fire control 

 problem. Hence, the geomstrical quantities fall 

 into certain main classes of quantities. Each of 

 the main classes of quantities is represented by 

 a class name. In each class, other geometrical 

 quantities, besides the basic quantity, are ex- 

 pressed by applying modifiers to the basic 

 quantity, as in the old system. The modifiers 

 express the way in which the quantity is meas- 

 ured. 



To illustrate, a class of quantities for ex- 

 pressing present target position is linear distance 

 between own ship and the target. This class of 

 quantities is called ranges. The basic geometrical 

 quantity in this class is the linear distance between 

 own ship and the target, msasured along the line 

 of sight. It is expressed by the capital letter R. 

 Another quantity in this class is the linear distance 

 between own ship and the target, measured in 

 the deck plane. This quantity is symbolized by 

 applying the modifier d (meaning measured in the 

 deck plane) to the basic range quantity R, forming 

 quantity Rd. 



The nomenclature assigned to represent the 

 basic geometrical quantity in each class, and 

 the letters and numerals used as modifiers are 

 listed (as mentioned previously) in the three 

 volumes of OP 1700. Extracts of Volume 2 of 

 OP 1700 (underwater fire control nomenclature) 

 are contained in Sonar Technician G_ 3 & 2. 



SONAR POSITION QUANTITIES 



When a target echo is received by a sonar 

 transducer, the target actually is not at the 



position indicated on the sonarscope, but at 

 some other location. This difference in target 

 positions is due to curvature of the sound beam 

 and to target movement during echo return time. 



The determination of actual target position 

 requires the application of corrections to the 

 sonar measurements. These corrections, which 

 are computed in the underwater fire control 

 system, consist of two position quantities: 

 apparent target position and past tai'get position. 

 (Target course and speed also are considered 

 in the problem.) Sonar position quantities are 

 illustrated in figure 7-3. The quantities are 

 expressed in the new fire control nomenclature. 



Two class quantities, range (R) and bearing 

 (B), are shown, together with the modifiers 

 necessary to express the appropriate measure- 

 ment. Quantities related to apparent target posi- 

 tion are represented by the lowercase letter a; 

 those related to past target position use the 

 letter p. The modifier h means the measurement 

 is in the horizontal plane; the modifier v refers 

 to the vertical plane. 



Apparent Target Position 



Apparent target position is the point from 

 which the sonar echo appears to come. It differs 

 from present target position because of refrac- 

 tion of the sound beam, and because of target 

 travel during the time required for the echo to 

 return to own ship. The dotted lines in figure 7-3 

 represent apparent position measurements. The 

 quantity Ba is apparent target relative bearing, 

 and Rha is apparent target range measured in 

 the horizontal plane. 



Past Target Position 



Past target position is tlie location of the 

 target when struck by the sound beam. In other 

 words, it is the position from which the sonar 

 echo actually comes. Past target position differs 

 from apparent target position because of refrac- 

 tion of the sound beam. It differs from present 

 target position because of target movement during 

 the time it takes the sound pulse to return to 

 own ship. 



Present Target Position 



Present target position is where the target 

 actually is located when the sonar echo reaches 

 own ship. It represents the distance traveled 

 by the target during the time it takes the sound 

 pulse to return to own ship from the target. 



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