THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

15.4 Velocity Profiles in the Sea 415Figure 15.3. Effect of latitude on sound-speed profile in deep sea.behavior of the surface layer near Bermuda. It shows how the temperature profilesvary, when the surface waters of the sea warm up during the course of asunny day and cool down during the night. These changes in temperatures affectconsiderably the transmission of sound from a surface-ship sonar, particularly inthe afternoon when echo ranging tends to be poorest. Figure 15.2b illustrates aseries of bathythermograms taken in the Bermuda area, showing how the seasonthermocline evolves during the summer and autumn. The effect of latitude onsound-speed profile in the deep sea is shown in Figure 15.3 by profiles for twodifferent locations in the North Atlantic at the same season of the year. At lowlatitudes (nearer the equator), the velocity minimum occurs at a depth of approximately3000 ft. At high latitudes the velocity minimum exists near the sea surface,and the main and seasonal thermoclines show a tendency to disappear from theprofile.In the shallow waters of the coastal regions and also on continental shelves, thevelocity profiles tend to become far less clear-cut and rather unpredictable. Thevelocities tend be greatly influenced by surface heating and cooling, changes insalinity, and the presence of water currents. Nearby sources of fresh water tend tocomplicate these effects and contribute to the spatial and temporal instability ofnumerous gradient layers.