On the parabolic equation method in internal wave propagation
  A parabolic equation for the propagation of periodic internal waves over varying bottom topography is derived using the multiple-scale perturbation method. Some computational aspects of the numerical implementation are discussed. The results of numerical experiments on propagation of an incident plane wave over a circular-type shoal are presented in comparison with the analytical result, based on Born approximation. 
M.Yu. Trofimov, S.B. Kozitskiy and A.D. Zakharenko