Computer-assisted interpretation

Abstract

The interpretation of sonar images, and more generally of remote-sensing images, has traditionally been performed visually by trained interpreters. This presents the distinct advantage of using the skill of the interpreter to limits which are often unattainable by computers. But there are also many disadvantages to a purely visual interpretation. First of all, it is subjective: two interpreters with different experience, or different skills, are likely to get different interpretations for some features, depending on their experience of the sonar used or of the environment studied. Visual interpretation is also time-consuming, and a longer amount of time spent on analysis does not ensure higher objectivity. Structural geologists all know that some morphologic trends will be highlighted, unwillingly and unconsciously, when the time spent on interpretation is too long. The other important disadvantage of visual interpretation is that it is qualitative. Objects are outlined, trends and patterns are shown. But their quantitative assessment requires either the interpretation to take place directly on a numeric support (with all the associated problems of screen size and limited range of scales available) or to scan and quantify the interpretation made on physical supports (paper maps, photographs, etc.). The last decade has seen many new useful tools for visualization of data; for example, in 3-D with the ubiquitous Fledermaus software (http://www.ivs3d.com/) and the use of immersive environments (based on virtual reality advances) like the ones used in seismic prospecting (e.g., Lin et al., 2000; Shell et al., 2006). Because of their cost and the necessary investment in hardware and software, these systems are still not within the reach of all sonar users, and they will still not replace the need for a full computer-assisted interpretation.