Caustic corrections using coherence theory

In the vicinity of a caustic the intensity is very different from that calculated on the basis of geometrical acoustics. Using the basic formulation of coherence theory we show here how the correct intensity may be obtained when the source has a finite (i.e., nonzero) size. We use a two-scale expansion to include the correction term to the geometric acoustic calculation (here already modified to include the effect of a finite source). It is shown that in the limit of a point source the results are the same as those previously obtained. Finally a numerical example is presented.