Analyzing acoustic imagery in 3-D: a case study

The U.S. Navy has always had an acute interest in the seafloor. It frames their battlespace, and knowledge of its features and characteristics can lead to tactical advantage. Modern survey technology, combined with precise positioning systems, has provided oceanographers more data than can be comprehended effectively. The task of scientific visualization is to represent the data both accurately and effectively. The application that is applied to the data must communicate the essential features within the data to the user. In the case of the seafloor, the ability to render the terrain in three dimensions (3-D) has not only made the data easier to interpret but provides a framework for intuitive displays of other data within the context of the submarine bottom. This case study demonstrates effective real-time rendering of gridded bathymetry, using a level of detail implementation to reduce the polygon count and provide a tool that is both efficient and portable. A navigable plan-view, graticule, and depth probe help to quantify the data within the application, which is primarily mouse-driven. The second part of this case study deals with applying acoustic imagery to the surface of the seafloor as a texture. High-frequency towed sensors are producing ultra-high-resolution imagery. These data can be manipulated rather painlessly in two dimensions (2-D); however, rendering a 3-D-textured surface in real time can tax even the strongest hardware. This application was designed to support mine warfare and mine countermeasures. To achieve interactivity with the data, a technique called 3-D clip-mapping or clip-texturing is applied. It leverages specialized hardware, which uses dedicated texture memory and can manage the varying resolutions created to facilitate interactive frame rates. Although some effort was expended to produce this application in OpenGL, it was decided to leverage the extensive development efforts devoted to Silicon Graphics, Inc.´s Performer product to accomplish this task. The Naval Oceanographic Office Major Shared Resource Center Visualization Center has made significant accomplishments toward the display of other ocean parameters within our 3-D ocean environment, such as ocean circulation, temperature, and bioluminescence. This case study will address only the applications developed for the bottom geometry, which, because of their efficiency, enable the incorporation of additional environmental information