ABSTRACT
Consider a two-dimensional wave field û(x, z, t) that in regions not occupied by sources satisfies the wave equation () ( ∂ 2 ∂ x 2 + ∂ 2 ∂ z 2 − 1 c 2 ∂ 2 ∂ t 2 ) u ^ ( x , z , t ) = 0. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203733998/5ed4f7c3-e1fb-41d9-a616-cbeb474272cd/content/eq143.tif"/>
