AEROGRAPHER'S MATE 3 & 2 



SOURCE 0.5 



TEMPERATURE 



55° 65° 



RANGE TO A SUBMARINE IN SHALLOW WATER. 

 ECHO IS DISCERNIBLE FROM BOTTOM REVERBERATION. 



SOURCE 



RANGE TO A SUBMARINE IN DEEP WATER 



Figure 16-7, — Range to a periscope-depth submarine in shallow and deep water. 



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axis are bent down by refraction; those starting 

 at angles below the axis are bent upward. The 

 procedure for locating this axis through 

 analysis is presented later in this chapter. 



CONVERGENCE ZONE, — This transmission 

 path, illustrated in figure 16-8 (C) is based 

 on the principle that sound energy from a 

 shallow source travels downward in the deep 

 ocean and is refracted at depth toward the 

 surface so that about 30 miles from the source 

 the sound signal again reaches the surface. 

 From there the signals continue as they are 

 reflected downward and then refracted upward to 

 reappear in the surface layer at successive 

 intervals of about 30 miles out to several 

 hundred miles. 



The conditions for convergence zone trans- 

 mission require that the sound velocity at depth 

 be equal to or greater than the velocity at 

 the surface and that water depth below this 

 second velocity maximum be sufficient for a 

 bundle of sound rays to be refracted so that 

 they converge at the surface in a small area. 



BOTTOM BOUNCE. — The three trans- 

 mission paths already discussed depend upon 



the restrictive conditions of the velocity 

 structure and the depth of the sound source 

 and receiver. Thus, if velocity gradients are 

 ignored, prediction of the paths is not possible. 

 The fourth path can be predicted roughly even 

 if these gradients are neglected. This path is 

 the bottom reflected path, commonly termed 

 bottom bounce. (See fig. 16-8 (D).) 



Bottom bounce is in part successful because 

 the angle of the ray path is such that the sound 

 energy is affected to a lesser degree by 

 velocity changes than the more nearly hori- 

 zontal ray paths of other transmission modes. 



Long range paths can occur with water 

 depths greater than 1,000 fathoms, depending 

 on bottom slope; but at shallower depths, 

 multiple bounce paths develop which produce 

 high intensity loss. It is estimated that 85 

 percent of the ocean is deeper than 1,000 

 fathoms, and bottom slopes are generally less 

 than or equal to 1 degree. On this basis, 

 relatively steep angles can be used for single 

 bottom reflection to ranges of approximately 

 20,000 yards. With steeply inclined rays, trans- 

 mission is relatively free from thermal effects 



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