TRANSDUCER HORIZONTAL 



289 



u 

 llJ 

 u. 



X 



bJ 

 O 







500 



1000 



1500 



2000 





 500 



1000 



1500 

 2000 



500 



1000 



1500 



2000 



25 



50 75 100 125 150 



NAUTICAL MILES 



175 



200 



225 250 



Figure 9. Depth of deep scattering layer at various positions. 



short ranges. Furthermore, the difference is usually 

 much greater in rough seas than in calm seas. Of 

 course, it is possible that the volume reverberation 

 obtained with the beam directed downward is less 

 than the volume reverberation with horizontal beams. 

 However, it is pointed out below that observed 

 values of 10 log m with horizontal beams are at most 

 only about 6 db greater than values of 10 log m meas- 

 ured with vertical beams. Thus, the conclusion is in- 

 escapable that in rough seas the short-range rever- 

 beration from horizontal pings is surface reverbera- 

 tion, that is, reverberation caused by scatterers near 

 the surface of the sea whose number and strength 

 are a function of sea state. 



14.2.1 Dependence on Range and 

 Oceanographic Conditions 



Analysis of reverberation records clearly shows 

 that the range dependence of surface reverberation is 

 itself a marked function of such oceanographic 

 parameters as ^ea state and temperature gradients. 

 For this reason, it is convenient to treat the effects of 

 all these variables together. The following section 

 summarizes the observational results of studies of 

 surface reverberation, which indicate that surface 

 reverberation tends to fall off with increasing range 

 much faster than predicted by the simple theory of 

 Chapter 12, and that the rate of decay increases 



I 



