P.M. Kendig 243 
is isotropic and its origin is not yet established. The second source of noise 
is generated by wave motion and whitecaps at the ocean surface. The equivalent 
surface radiator is highly directional in the vertical plane when azimuthal ef- 
fects are averaged. The directionality can possibly be attributed to the ocean 
waves and swells functioning in a manner analogous to angular focusing re- 
flectors. In addition, the ocean swells impede transmission at shallow trans- 
mission angles in directions normal to the wavefronts of the swells. 
It is further postulated that the noise intensity at a given point in the ocean 
caused by the equivalent surface radiator arrives by both a direct-ray path and 
single-bounce path experiencing specular reflection at the ocean bottom. 
By taking into account the bottom-reflected energy and the attenuation due 
to spherical spreading and absorption occurring over the separation between 
radiator and receiver, it is possible to evaluate S(6) which is the radiated -noise 
intensity due to unit incremental radiating surface at one yard. The quantity 
S(@) is markedly directional in the downward direction and can be represented 
approximately by the expression: 
4 ((cos 9Y2° — 9/1 F420 < A < 70° 
© =) cos?6 for70° < 6 < 90° 
Figure 13.6 is a plot of a reasonable approximation of S(@) superimposed on the 
experimental data. 
OCEAN SURFACE 
SS 
Fig. 13.6. Surface source level re normal to ocean surface, 
