Global Model for Sound Absorption in Sea Water. Part 2. GEOSECS pH Data Analysis

摘要

Ionic relaxations involving magnesium sulfate, boric acid and magnesium, carbonate are known to account for sound absorption in sea water. Regional dependence of sound absorption has been shown to be caused mainly by the pH-dependence of the boric acid relaxation. In the nominal sea water pH range 7.7-8.3, the magnitude can be expected to vary over neatly a factor of four at lower frequencies. Since pH varies with depth as well as locations, net absorption will also depend on the ray paths. An interim global model, based on published pH contours for the World Ocean, has been proposed. Correction factors for the sound-channel, convergence-zone and surface-duct modes are provided by individual contour charts. However, if there is no clearly dominant propagation mode, integrations of loss over all ray paths may be indicated, which requires profiles of correction-factor vs depth. Part-2 reports analysis of pH data obtained during the GEOSECS expeditions 1972-1978. The purpose is to check the accuracy of the global model contous charts and to investigate methods of estimating profiles of correction-factor vs depth. PH profiles for all the stations reported in the Atlantic, Pacific, and Indian Oceans are presented graphically and derived correction factors are listed in tables. Correction-factor contour charts at depths 0, 0.5, 1, 2, an 4 km are also developed and agreement with the earlier versions appears to be within expected experimental error. The five values provided by the contour charts should permit reasonably accurate estimation of the correction-factor profiles in most of the World Ocean.