The development of sonar imaging technology has undergone rapid change in the last five years. The reason for this is due mostly to the availability of low cost, high performance PC technology. The application of PC technology is evident everywhere today, but, for sonar image processing this has been taken a step further. The application of newly developed image processing techniques to sonar data not only means that things can be done more efficiently and with greater accuracy, but they can also be done automatically
This paper will outline the application of automated sonar data interpretation to inspection (subsea pipeline inspection), survey (site investigations, oceanography) and search and recovery It will describe some of the methods used for automatically identifying and tracking subsea structures, seafloor characterisation and target searching The methods described vary from conventional image processing techniques to more advance texture analysis and image segmentation Applications of these automated interpretation techniques will be outlined along with some success stones since their introduction
A clear result for automated interpretation of digital sonar image data is the improvement in accuracy and consistency of results. In the North Sea, pipeline operators have been able to tighten their inspection criteria significantly. Therefore automated digital image processing is here to stay
The offshore survey industry has become very complex and highly technical with great advances in positioning, navigation and sonar systems. Sonar, or acoustic, techniques are used to investigate and chart the sea floor and its subsurface for commercial, scientific and environmental motives The potential for the application of powerful computing power and image processing techniques to sonar survey activities is enormous In general, sonar systems are used to investigate the sea floor, and what lies beneath it In particular, sidescan sonars are used to provide information on seabed features such as coral, seabed structure, or searching for subsea structures, ship wrecks, military targets etc. [I]
Before digital data recording was available, sidescan data was recorded to thermal paper resulting in long rolls of sonar images that must be interpreted by a trained geophysicist This is quite an involved task requiring the geophysicist to determine the position of seabed features using navigation information, collate informatoon into a report and then somehow present the information in chart form either manually or electronically. In addition, the geophysicist must manually calculate and correct the slant range image and seabed feature dimensions Interpretation may be limited by the quality of the paper record, which reduces reliability and accuracy
The use of computers can clearly revolutionise sonar data interpretation by providing improved display, interactive interpretation and digital recording Figure 1 gives an overview of data flow and processing in a typical computer based sonar data acquisition and interpretation system.
There are obvious and immediate advantages of a computerised display over conventional paper records. Enhancement tools to optimise image contrast and colour will improve image quality and therefore improve interpretation.