Mathematical models for passive imaging II: Effective Hamiltonians   associated to surface waves
  In the present paper which follows our previous paper ``Mathematical models for passive imaging I: general background'', we discuss the case of surface waves in a medium which is stratified near its boundary at some scale comparable to the wave length. We discuss how the propagation of such waves is governed by effective Hamiltonians on the boundary. The results are certainly not new, but we have been unable to find a precise reference. They are very close to results in adiabatic theory. 
Yves Colin de Verdiere