Except in the vicinity of the minimum loss the propagation losses for the summer 

 and intermediate profiles are 10-30 dB greater than for the winter profile in the frequency 

 range displayed. At optimum frequencies the propagation losses are about the same for the 

 three profiles. The results for the summer profile (Figure 4.2) and the intermediate profile 

 (Figure 4.3) differ mainly only at the frequency extremes, below 200 Hz and at about 700 

 Hz and longer ranges. The decrease in loss near 250-300 Hz is more abrupt for the 

 intermediate profile and the decrease in loss near 700 Hz (Figure 4.3) is shifted to 900 Hz 

 in Figure 4.2 for the summer profile. The most significant difference between these two 

 profiles is that the sound speed at the source depth of 25 m is greater by about 6 m/s for 

 the intermediate profile (see Figure 3.2). 



4.1.2 Strait of Juan de Fuca 



The water column and the sea floor sediments in the area of the Strait of Juan de 

 Fuca site were modeled for propagation loss computations as shown in Tables 4.3 and 4.4. 



Winter 





Fall 



Summer 



Depth, 



Sound Speed, 



Depth, 



Sound Speed, 



Depth, 



Sound Speed, 



m 



m/s 



m 



m/s 



m 



m/s 







1480.3 







1489.4 







1497.5 



25 



1482.2 



30 



1491.1 



10 



1494.5 



75 



1483.8 



50 



1482.3 



20 



1482.5 



130 



1484.5 



100 



1479.6 



30 



1480.3 







130 



1479.8 



75 

 130 



1477.7 

 1477.9 



Table 4.3. Sound speed in the water column. 







Sound 



Sound 











Bottom 



Sediment 



Speed 



Speed 



Gradient 



Absorption 



Absorption 





Layer 



Depth, 



Top, 



Bottom, 



Top, 



Top, 



Bottom, 



Density, 



Number 



m 



m/s 



m/s 



s-1 



(dB/km)/Hz 



(dB/km)/Hz 



g/cm^ 



1 



0.0 



1529.0 



1590.0 



1.22 



0.15 



0.16 



1.61 



2 



47.0 



3000.0 





-0.1 



0.1 





2.3 



Table 4.4. Sediment parameters used in computations. Strait of Juan de Fuca. 



Sediment sound speeds are given for the winter profiles. The adjustment is made 

 for the other seasonal profiles to keep the ratio of sound speeds (surface sediment to bot- 

 tom water) equal to 1 .03. Density in the water is assumed to be 1 .03 and a constant value 

 in each sediment layer. 



Propagation loss for optimum receiver depth as a function of frequency is shown 

 in Figure 4.6 (winter), Figure 4.7 (summer) and Figure 4.8 (fall) for the different seasonal 

 profiles. Optimum frequencies of propagation are about 300 Hz for the positive gradient, 

 winter conditions, about 125 Hz for the non-positive summer profile and 900-1000 Hz for 

 the fall profile. The propagation losses are much less for the winter profile, about 10 dB 

 at optimum frequency and 10-50 dB less elsewhere. Propagation is slightly better at opti- 

 mum frequency for fall compared to summer but is lower at other frequencies. 



43 



