11-10 



INTERFERENCE RANGE 



FIGURE II-2 SCATTERING BY THE OCEAN MICRO-STRUCTURE 



Inside the focusing range we might expect an analysis in terms of ray 

 acoustics to be adequate, since the scattered waves are all in phase. Rays are 

 focused or defocused by individual inhomogeneities but do not interfere with one 

 another. Beyond this range, wave acoustics become necessary. In Chapter IV 

 we treat the general scattering formulation and obtain both the ray and inter- 

 ference results as limiting expressions. An excellent treatment based on ray 

 acoustics alone and applicable in the focusing range may be found in Chernov, 

 Part I. 



The scattering from a single weak inhomogeneity is examined in Sec- 

 tion IV-B. It is shown that the scattered pressure field is indeed highly direc- 

 tional when kR > > 1 . The ratio of the scattered to the incident pressure in the 

 forward direction, i.e. , in the direction of propagation of the incident plane 

 wave, is shown to be 



P,-, 



k^ tIvI 



(II- 4) 



artbur Sl.littleJnt. 



S-7001-0507 



