I

Area

4nr 2

j Spherical spreading

2nrH

WWWY* AWWWXWW

2nr2H

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* Source Cylindrical spreading

Figure 3.7 Geometry for (a) spherical spreading and (b) cylindrical spreading.

(Urick, 1983; Principles of Underwater Sound, 3rd edn; reproduced with permission of McGraw-Hill Publishing Company.)

As a matter of convention, 0 is referred to as the incidence angle while 0 is referred to as the grazing angle.

In a homogeneous medium, acoustic TL varies as the inverse of the range squared. This relationship is easily derived, as demonstrated below. Let I = intensity, P = power and A = area, then:

For spherical spreading (see Figure 3.7(a)):

where r1 and r2 are the radii of concentric spherical sections. Power (P) is conserved; therefore, P1 = I1A1 = I2A2 and:

but r1 represents a unit reference distance and thus: I1

0 0

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