Analysis and Ranking of the Acoustic Disturbance Potential of ...

Report No. 6945
BBN Systems and Technologies Corporation
Table 4.2. Parameter Values for IFD Slope Model.
Source ha. 1 (10 b) Source ha. 2 (3.3 k ~ ) Year-Shore (20 It)
Type Slope Water Layer 1 Layer 2 Water layer 1 layer 2 Water Layer 1 Layer 2
A. Bottom Layer Thickness, m (see Fig. 6)
1 -0.004 37 25 >200 13 11.7 >200 1 5 > 200
2 -0.01 9 1 2 >200 3 1 0.8 >200 1 0.1 >200
3 -0.01 70 25 >200 20 5 >200
8. Bottom Material Parameters
Bottom Type 1 Bottom Type 2 Bottom Type 3
Water Layer 1 Layer 2 Water Layer 1 Layer 2 Water Layer 1 Layer 2
Sound Speed 1470.5 1700 1900 1471 1700 4000 1471 1700 1900
(m/sec )*
Density 1000 1800 2200 1000 1800 2800 1000 1800 2200
(kg/cu .m)
Attenuation 0 0.13 0.13 0 0.13 0.04 0 0.13 0.13
(dB/uavelength )
Layer 1 material silt/fine sand silt/fine sand silt/fine sand
Layer 2 material sand/gravel basalt sand/gravel
*Sound speed at surface 1470 m/sec, sound speed at 90 m, 1472 m/sec, linear gradient.
silty, very fine sand over a basalt rock sub-bottom. The model is based on
data reported for Bering Sea regions by Mackenzie ( 1973). Bottom Type 3
represents conditions further off shore along the north shore of the Alaska
Peninsula, Unimak Island and parts of the coastline near the Shumagin
Islands. It features an initial depth of 70 m which shoals to 20 m over a
distance of 5 km. The layer structure is similar to that of Bottom Type 1,
with a different slope geometry as shown in Fig 4.4B.
The neutral gradient sound speed profile shown previously in Fig. 4.2 was
used for the pinniped related model study. This is representative of Bering
Sea conditions in spring before the warm summer surface layer has developed.
For the gray whale related modeling, the surface layer profile typical of late
summer conditions was also used.
The results of the IFD Model study using the Type 1 Bottom parameters are
shown in Figures 4.5A through 4.5D. Figure 4.5D presents the TL characteristics
for the two source positions plotted to show TL versus distance from the
beach. This is presented as a more relevant format than the usual TL plot
showing TL versus range from the source position.