Acoustic Wave Propagation in an Underwater Sound Channel 1. Qualitative Theory

We give a qualitative study of wave propagation in an inhomogeneousmedium principally by geometrical optics and ray theory. Theinhomogeneity is represented by a sound-speed profile whichis dependent upon one coordinate, namely the depth; and we discussthe general characteristics of wave propagation which resultfrom a source placed on the sound channel axis. We show thatour mathematical model of the sound-speed in the ocean actuallypredicts some of the behaviour of the observed physical phenomenain the underwater sound channel. Using ray theoretic techniqueswe investigate the implications of our profile on the followingcharacteristics of SOFAR propagation: (i) the sound energy travellingfurther away from the axis takes less time to travel from sourceto receiver than sound energy travelling closer to the axis,(ii) the focusing of sound energy in the sound channel at certainranges, (iii) the overall ray picture in the sound channel.