Deep-ocean ray transmissions over convergent and divergent sloping bottoms

Abstract

Surface-reflected/bottom-reflected transmissions over a slowly sloping bottom in a deep ocean are investigated using ray theory. For convenience, sound speed is taken to be bilinear with depth in the water, while the bottom structure is assumed to be uniform. The sound source and receiver are located on or near the ocean boundaries, and the effects of bottom slope on ray geometry, per-ray travel time, and incoherent total-field amplitude are examined. For transmission ranges of tens of km, and for typical deep-ocean slope inclinations, travel time may change by about 1.0 s, relative to its value for a horizontal bottom. The time difference between ray arrivals decreases (increases) in the divergent (convergent) channel. Principal effects of bottom slope on total-field amplitude arise primarily through bottom-loss modifications, rather than through spreading loss. An inclination-angle magnitude of only 0.25° is shown to cause a decrease of about 8 dB (increase of about 4 dB) in the incoherent amplitude in the convergent (divergent) channel, for ranges of about 100 km. Changing bottomed receiver location in a convergent channel, in order to improve source detectability, is shown in an example to be much more effective than in the case of a horizontal bottom. In a corresponding divergent channel, however, the strength of the acoustic reception is much less sensitive to variations in receiver location.