Ill- 91 



In both cases, very close agreement was found between the theoreti- 

 cal and experimental scattering directions . La Casce measured these by noting 

 the directions which corresponded to peaks in the reflected sound. He found the 

 observed angle generally to be within 2° of the expected angle; only rarely was 

 the difference as large as 3 ° . Leporskii, using a more precise technique, found 

 even closer agreement. Leporskii's results are shown in Figure III-30, which 

 compares the expected and experimental angles. The data reported is for inci- 

 dent sound with k ~1 . 7mm"''' (for several different scattering orders), and for 

 surfaces with p =~0.41 mm"''', h~ 1.0 mm. Figure III-30a refers to surfaces 

 with sinusoidal corrugation, while Figure Ill-SOb deals with sawtooth corruga- 

 tions . (Other data of Leporskii relating to scattering directions is shown in 

 Figures III-39 and III-41). 



Figures III-31 through III-38 show some of La Casce and Tamarkin's 

 experimental results and compare these with the various theories . The data is 

 for the amplitudes A^ and A.^ . Two surfaces are considered, each of the form 

 S(x) = h cos px. Surface A has p = 3.12 cm"''", h = 0.24 cm while surface B has 

 p = 3.08 cm-''" and h = 0.15 cm. Measurements were made at 0° and 40° angles 

 of incidence. The order of presentation is as follows: 



Figure 



Component 

 A 







Surface 

 A 



Angle of Inc 

 0° 



Theoretical Models Compared 



III-31 



1,2,3,4 



III-32 



A 

 o 



B 





0° 



1, 2, 3, 4, 5 



III-33 



A 







A 





40° 



1,2,3,4 



III-34 



A 







B 





40° 



1,2,3,4,5 



III-35 



A-i 



A 





0° 



1,2,3 



III-36 



A-i 



B 





0° 



1,2,3,5 



III-37 



A-i 



A 





40° 



1,2,3 



III-38 



A-: 



B 





40° 



1,2,3,5 



*1. Rayleigh 





3. 



Brekhovskikh 



5 . Heaps 



2 . Rayleigh (La Casce) 





4. 



Parker 





The experimental data exhibit a peaking, or nodal, behavior. All of 

 the theoretical models predict this fairly well, suggesting that the Bessel func- 

 tions used in the models are appropriate for describing the scattering magni- 

 tude . All the models predict roughly the same behavior, and there is nothing 



Arthur B.littleJnt. 



S-7001-0307 



