As in all of the computational models in this report, the listed sediment sound 

 speeds are for the winter profile with the ratio of sound speeds (surface sediment/bottom 

 water) equal to 1.12 for Lands End and adjusted accordingly for the summer profile. 



Calculated minimum propagation losses as a function of frequency are shown in 

 Figure 4.1 1 (winter profile) and Figure 4.12 (summer). The positive gradient conditions 

 (winter, Figure 4.1 1) do not show much frequency dependence over the range shown. How- 

 ever, optimum frequencies of propagation are about 300 Hz for the winter profile (based 

 on the propagation to 150 km) and about 900 Hz for the summer conditions. Also propa- 

 gation losses are 10 dB greater for the summer profiles. The irregularities in the curves in 

 Figure 4. 1 2 (summer profile) are due to a near-isovelocity portion of the profile above 

 20 m (see discussion in Section 4.2.1). 



4.1.5 Korea Strait 



The computational models for the Korea Strait site are given in Table 4.9 for the 

 water column and in Table 4.10 for the sediments. 



Winter 



Summer 



Depth, 



Sound Speed, 



Depth, 



Sound Speed, 



m 



m/s 



m 



m/s 







1503.0 







1536.3 



128 



1505.24 



20 



1534.3 







30 



1527.5 







50 



1517.7 







128 



1507.5 



Table 4.9. Sound speed in the water column, Korea Strait. 







Sound 



Sound 











Bottom 



Sediment 



Speed 



Speed 



Gradient 



Absorption 



Absorption 





Layer 



Depth, 



Top, 



Bottom, 



Top, 



Top, 



Bottom, 



Density, 

 g/cm 



Number 



m 



m/s 



m/s 



s-1 



(dB/km)/Hz 



(dB/km)/Hz 



1 



0.0 



1759.0 



1787.0 



9.12 



0.5 



0.4 



1.93 



2 



3.0 



1600.0 



2327.0 



0.42 



0.1 



0.07 



1.53 



3 



1003.0 



4100.0 





-0.1 



0.03 





2.33 



Table 4.10. Sediment parameters used in computations, Korea Strait. 



The sediment sound speeds are given for the winter model and should be adjusted 

 to keep the ratio of sound speeds (surface sediment/bottom water) equal to 1.17 before 

 calculations for the summer (or another) profile are performed. The density in the water 

 column was 1 .03 and the densities in each sediment layer are assumed constant within 

 layers. 



The sound speed at the top of the second layer of sediment in Table 4. 1 is not 

 the same as in Table 3.10. Difficulties in the normal mode calculations were experienced 

 with the lower velocity. This sediment model is similar to the North Sea sediments in that 

 each has a surface layer of fine sand of about the same sound speed and layer thickness 

 (2 m for North Sea versus 3 m here) and no difficulties were experienced for the North 



48 



