ON WAVE PROPAGATION IN NON-UNIFORM MEDIA

In this paper,the results are analysed on wave propagation in non-uniform media which were studied by Lighthill,Whitham and some others.It is found that when the phase of wave is expressed as that of near plane wave i.e.θ=k(X,T)x-ω(kX,T),X,T)t where X=εx,T=εt,ε is a small parameter,k,ω are local wavenumber and frequency,then we can get ∂k/∂T+∂ω/∂X=∂Ω/∂X.This means that the phase does not satisfy the principle of continuity as proposed by them.With this result,it is pointed out that the wavenumber is always constant along rays while frequency is variable.This is different from that obtained by Lighthill and others.The causes for these differences are discussed in the paper.