Ill- 11 



As the value of ka approaches 1.0, the simple Rayleigh solution (III- 15) 

 no longer holds and more terms of the series solution must be considered. In 

 this region, which may be termed the critical region, some of the general char- 

 acteristics of the backscattering in the Rayleigh region are still apparent. Fig- 

 ures III-2a and III-2b show the dependence of R on the relative sound velocity h 

 and acoustic radius (ka), while Figures III- 3a and III- 3b show the dependence 

 of R on the relative density g and acoustic radius. Comparing the figures, the 

 most striking difference is the presence of large slopes for the small values of 

 h compared with the gradual rate of change of R with the relative density g. 

 The difference between the dependence of R on h and g seems to become even 

 more pronounced in this region than in the Rayleigh region, particularly for the 

 larger values of (ka). 



g- 10 



.4 .6 1,0 14 2D 3.0 4.0 



ka 



g=i.2 



.4 .6 10 1.4 20 3.0 4.0 



ka 



FIGURE III-2 THE REFLECTIVITY R AS A FUNCTION OF THE RELATIVE SOUND 



VELOCITY h AND ACOUSTIC RADIUS Ka (AFTER ANDERSON) 



b. 



R 1- 



h = l.O 



4 .6 1.0 1.4 2.0 3.0 4.0 



ka 



h = 1.2 



4 .6 1.0 14 2.0 3.0 4.0 



ka 



FIGURE III-3 THE REFLECTIVITY R AS A FUNCTION OF THE RELATIVE DENSITY 



g AND THE ACOUSTIC RADIUS Ka (AFTER ANDERSON) 



Arthur Sl.1ltttlc.3nc-. 



S-7001-0307 



