INTRODUCTION TO SONAR 



in stern traces, inasmuch as it is farther away 

 than the submarine itself; doppler is liigh. 



One of the best ways to identify a TRR trace 

 is to decide whether it is abeam trace. Normally, 

 a good look at the trace is all that is necessary to 

 resolve this question, but you should also listen 

 for doppler. If doppler is low, the target aspect 

 is either quarter or stern-on. If high, the target 

 is either bow or direct-bow. Remember, though, 

 that doppler depends on motion as well as aspect 

 of the target. 



Sonar echoes also are returned from other 

 submerged objects besides submarines. Usually 

 nonsubmarine traces are recognized easily. 

 Echoes returned from a wake, for example, 

 ordinarily are not accompanied by doppler, the 

 traces are quite long, and the entire series of 

 traces consists of irregular waves. 



Stationary targets, such as nonmobile counter- 

 measures (a bubble is an example) are very 

 sharp and regular in the series of traces, but 

 there is no doppler, and the range rate equals 

 own ship's speed. 





HORIZONTIL RANGE 



.% HORIZ 

 -- , RANGE 

 5 *- RATE 



'~ KNOTS 



^V°^^ MM'/'/;/;//. 



INTERPRETING DIAL READINGS 



Sonar Technicians must be able to interpret, 

 and sometimes interpolate, sonar and fire control 

 equipment dial settings. Information to be read 

 from these dials includes such values as range, 

 range rate, target course and speed, and many 

 other fire control values. Normally, two types of 

 dials are used. They are disc dials and ring dials. 



A disc dial is simply a flat, circular plate 

 secured to a shaft, and inscribed with values of 

 the function it serves. A ring dial is circular- 

 shaped also, but has a hollow center to permit 

 placing a disc dial within it. An example of the 

 use of these dials is shown in figure 7-24. 



The top dial group displays target informa- 

 tion. The bottom dial group shows own ship data. 

 The counters between the two dial groups show 

 horizontal sonar range. The dial to the left of the 

 range counters indicates horizontal range rate. 



Target Dial Group 



Two concentric dials make up the target dial 

 group. They are a ring outer dial and a disc inner 

 dial. Both dials are graduated in 5° increments and 

 are numbered at 10° intervals.Target angle (144°) 

 is read on the inner dial against the fixed index at 

 the bottom of the dials. Target course (072°) is 





fJ ^^ iz o? , \ ' 



51.108 

 Figure 7-24. — Own ship and target dial groups. 



read on the outer dial against the zero graduation 

 of the inner dial. 



Own Ship Dial Group 



The own ship dial group consists of an inner 

 disc dial, an inner ring dial, and an outer ring 

 dial. The two inner dials are graduated in 5° 

 increments and are numbered at 10° intervals. 

 The outer dial has only a diamond marker and 

 the words COURSE ORDER inscribed. The inner 

 disc dial shows relative sonar bearing (002°) 

 against a fixed index at the top of the dials. The 

 inner ring dial shows own ship's course (032°) 

 against the zero graduation of the inner disc 

 dial. Course order (039°) is read on the inner 



130 



