Measurements of normal-mode amplitude functions in a nearly-stratified medium
In normal-mode treatments of acoustic propagation in nearly-stratified media, calculations are frequently based on the perfectly-stratified medium model, in which symmetry permits separation of the wave equationo In these treatments the ass~ption is made that the normal-modes adapt to local conditions and that the modes are not coupled by the changing environmento This assumption is frequently referred to as the adiabatic approximation. An experiment was performed in a shallow water area near Jacksonville, Flao, in which observations were made of individual normal modes propagating over two sloping bottom tracks o Over the first track the water depth increased from 30 m at the source to 41 m at the receiver, with the maximum bottom slope (0.3°) at the receivero Isovelocity conditions prevailed on this track. Over the second track the water depth decreased from 120 m to 42 m with the maximum slope (0.3 P-0.9°) at the source positionso The vertical sound speed gradient on this track was slightly negative at the receiver and more sharply negative at the sourceo In both cases the constant depth model gave the vertical pressure distributions observed, in agreement with the assumption that the modes adapt to local conditions. Results from the first track are in agreement with the adiabatic approximation, however, propagation over the second track indicates the presence of mode coupling.
SourceIn: Ocean Acoustic Modelling (SACLANTCEN Conference Proceedings CP-17), Part 7, 1975, pp. 34-1 - 34-9.
Wolf, S. N.