INTRODUCTION TO SONAR 



71.7 

 Figure 3-12. — Target aspect. 



Figure 3-12 shows the five basic target aspects 

 and their associated doppler. The degree of 

 doppler is dependent on target speed. For 

 example: Doppler of a direct bow target with a 

 high closing speed would be reported as "marked 

 up." 



Target aspect is best described as the relative 

 position of the submarine with respect to the 

 sound beam. Perhaps the easiest way of deciding 

 which aspect the submarine is presenting is to 

 visualize it in the center of four quadrants and, 

 by the process of elimination, solve for the 

 proper quadrant. This procedure gives a rough 

 aspect, and doppler and bearing drift will further 

 define the exact aspect. Look at figure 3-13 to 

 see how this solution is accomplished. Assume 

 that your ship is headed for the target, and 

 that initially you have a steady bearing with 

 high up doppler, which indicates that the ship 

 and the submarine are headed directly for each 

 other. Next, you detect a bearing drift to the 

 right, with slight up doppler. Quadrants A and 

 B are eliminated because a target in either 

 quadrant would have down doppler. A target in 

 quadrant C will have up doppler, but the bearing 

 drift will be to the left. Therefore, you would 

 report "Starboard bow aspect." 



As the ship attacks, she makes minor course 

 and speed changes, but these changes have 

 little or no effect on target aspect or doppler. 

 If the ship circles the submarine, however, or 

 if the submarine makes a change in course, 

 target aspect will change. A change in doppler 

 is the first indication that the submarine is 

 changing course, and this change must be re- 

 ported immediately. As soon as the new aspect 

 can be determined, it also must be reported. 

 During an antisubmarine attack (or series of 

 attacks), aspect changes often. The sonar oper- 

 ator's job is to detect, evaluate, and report 

 each change as it occurs. 



COMPUTING TARGET ANGLE 



Target angle, which is a relative bearing, 

 gives more precise information on the course 

 of a ship or submarine than does target aspect, 

 but target angle is more difficult to obtain 

 than is target aspect. In considering a destroyer 

 making an attack on a submarine, target angle 

 is the relative bearing of the destroyer from 

 the submarine. 



30 



