MINIMUM DIFFRACTION SPREADING OF DISTANT INSONIFIED ZONES IN AN OCEANWAVE-GUIDE - A QUASI-OPTICAL THEORY

It is demonstrated that the ray theory describes the formation of the narrowest insonification zones, but, without any regard to their depen dence upon frequency. The WKB approximation for the field in the mode representation is shown to properly describe the minimal spread of ins onified zones at a specific frequency,which depends upon the depth of the communicating points. An equation for this dependence is obtained.