\ 



— 1 — 1 1 



SUMMER ^ 





- 



/^ / 





• WINTER^/ / 



- 



/ / 





\ y'^— INTERMEDIATE 





\/ 



- 



1 





1 1 NORTH SEA 



1470 



1 490 1 500 



SOUND SPEED, m/s 



Figure 3.2. Characteristic sound speed profUes 

 found at the North Sea site. 



From the table, the probabiUty of encountering a surface duct environment is 

 93.3 percent in the fall or winter seasons, while in the spring or summer the occurrence of 

 surface ducts is only 28.7 percent. 



The properties of the sediments are given in Table 3.2. R is the ratio of the surface 

 sediment sound velocity to that of the bottom water (for all profiles in that area) and the 

 sound velocity given in the sediments is greater by that ratio for the winter sound speed 

 profile. The attenuation a is in units of (dB/km)/Hz and thus must be multiplied by the 

 frequency to obtain absorption. 











Compressional 











Thickness, 



Depth, 



Velocity, 



Attenuation, 



Density, 



Layer 



Material 



m 



m 



m/s 



(dB/km)/Hz 



g/cm^ 



Sea Floor 









R= 1.19 







1 



Fine sand 



2 



Sfc 



1760 



0.47 



2.05 









2_ 



1778 



0.42 



2.05 



2 



Mudstone 



2000 



2+ 



1700 



0.12 



1.74 









1000 



2000 



0.07 



2.1 









2002- 



2300 



0.02 



2.2 



3 



Sandstone 





2002+ 



2540 



0.02 



2.2 



Table 3.2. Sediments at the North Sea site. 



20 



