The effect of undersea ridges on SOFAR signals
Leon Krige
Department of Oceanography University of Cape Town
Analysis of shot signals over a 4.4 Megametre line between Cape Town and Ascension show that reflections off the sea bottom lengthen the duration of the signal at the receiver. Ray trace modelling shows that many reflected eigenrays are probable. The direct and reflected components of the signal are not readily distinguishable by inspection of the signals arriving at the receiver. The arrival time of the reflected rays, unlike that of direct rays, cannot be simply equated to the depth of the ray turning points. Rays with launch angles less than about 12 degrees tend to have small grazing angles and mimic rays without reflections. Rays with larger launch angles are reflected more often and are widely scattered in arrival time. Some reflected rays may overlap the arrival time period of direct rays and contaminate the temperature information. Since similar ridges occur in most ocean basins, the problem for ocean acoustic tomography will be to identify and avoid these reflected rays.
