Ill- 92 



in the experimental data which indicates any one as being the most suitable. 

 Heaps' approach, which neglects the damped waves, seems to give the best re- 

 sults . The poorest agreement occurs for the larger angle (40°) of incidence. 

 In general, experimental results for surface B agree with the theoretical pre- 

 dictions better than those for surface A. This is to be expected; since B has a 

 smaller value of h, the condition on (kh) and the slope will be better satisfied. 



Leporskii has compared his experimental data with the predictions of 

 the Brekhovskikh (Ref. III-21) and Lysanov (Ref . III-22) models. Since the sur- 

 faces and frequencies are quite different, the data cannot be compared directly 

 with La Casce's. Furthermore, since results are presented for only a few fre- 

 quencies, we cannot observe the variation in scattering amplitudes with changes 

 in frequency, as shown in Figures III-39 through III-41 . On the other hand, 

 Leporskii's technique permits him to observe several of the scattering orders. 



Figure III-39 illustrates the theoretical and experimental agreement 

 for the Brekhovskikh model, with the dotted lines giving the theoretical values 

 and the solid lines the experimental results. The dashed lines are the bounda- 

 ries of the sectors within which the Brekhovskikh theory is claimed to be valid . 

 The arrows pointing towards the center of the pattern show the direction of the 

 incident wave; the arrows pointing away show the direction of specular scatter- 

 ing. As can be seen from the figure, the agreement is qualitatively good; how- 

 ever, in each case there is significant disagreement for the magnitude of some 

 scattering order. The conditions of the theory were well satisfied in the experi- 

 ment; hence some inadequacy apparently remains in the theoretical development. 



Figures III-40 and III-41 compare the prediction of the Lysanov model 

 with Leporskii's experimental results. Figure III-40 compares the magnitudes 

 of the expected and observed amplitudes for various orders of scattering surfaces, 

 frequencies and angles of incidence. Though not stated, the conditions are pre- 

 sumably the same as in the analysis of the Brekhovskikh model. Figure III-41 

 illustrates the scattering of various orders. As with the Brekhovskikh model, 

 the agreement is qualitatively good; however, the scatter shown in Figure III-40 

 suggests that there may still be significant discrepancies between theoretical 

 expectation and experimental observations . 



Srtbur Sl.littlcJnir. 



S-7001-0307 



