





\ 1 





*- SURFACE 



100 



i 



/ DUCT 









E 200 



1- 



( 





DEEP 

 DUCT 



LU 



Q 300 



\ 





400 



_ ^r 





500 



/ , 



1 



1 520 1 530 



SOUND SPEED, m/s 



Figure 7. A five-layer approximation to the sound speed 

 of a surface duct overlying a refractive duct. 



-J 1529.5 — 



1529.0 - 



1150 1200 1250 1300 1350 1400 1450 

 FREQUENCY, Hz 



Figure 8. The real part of the eigenvalues as continuous 

 functions of frequency for the profile of figure 7. 

 Some mode numbers are given. The first three modes 

 for the surface duct only (SD) are shown as broken 

 lines. That for mode 1 coincides with an existing line. 



37 



