Sidescan sonars have been important tools in offshore surveys for many years. Traditionally the sonars produce paper records on-line. These range from simple systems displaying only the raw sonar signal to more sophisticated systems. The latter correct the sonar signal for slant range and adjust the paperfeed according to vessel speed information. These sonar images come close to a scale-corrected picture, provided that profile lines are completely straight and speed data input to the system is of a high accuracy. The paper sidescan sonar record can then be interpreted by a skilled surveyor, geologist or geophysicist who can ‘tanslate’ his or her interpretation into a mapable form. In this process it is normal practice to define areas of common seabed features, identify major elements and, after correcting for geometrical distortion, manually plot a seabed feature map. A basic weakness in the seabed feature maps that are produced is the lack of fine detail that can be successfully displayed-for example the gradational nature of sediment boundaries. On complex areas this transformation of information from sonar paper records to seabed feature maps is a arduous job.
The first basic aim was that the computer-aided mapping of sonar (CAMOS) should present the true track of the sonar towfish for survey lines that are not absolutely straight due to survey conditions, or for survey line following an intended curved path-for instance while tracking a pipeline. The second aim was that the CAMOS software to present several adjacent sonar profiles on one map as a mosaic. Thraditionally sonar mosaics have been created using scissors and glue.
These goals can not be achieved on a real-time on-line system. A post-processing system requiring computer resources was needed in order to deal with the huge amount of sonar data. The concept should be flexible with new opportunities to control and present sonar information. On the other hand, running the software becomes expensive, due to operator time and computer consumption.
The software was designed to work with the company's existing computers and sonars. It is therefore not at this stage a generalized software product that will work with any computers or sonars.
Figure 1 is intended to illustrate a CAMOS end product, An artificial survey track line following a 270 degree curve has been created. A sonar profile was applied to this line to show the response utilizing CAMOS software. Note that this is not a true survey line. The intention is to show the ability of CAMOS to display scale-corrected sonar images of any predicted or non-predicted curved survey paths.
Fig 1 CAMOS example of a sonar image following an artificial profile track (available in full paper)
This chapter will discuss the equipment used in the development of the CAMOS software. Geoteam operates survey vessels suitable for undertaking a broad spectrum of marine site evaluation projects. A computer-processing department in Oslo performs post-processing of navigation, position fixing, hydrographic survey data and seismic. It was therefore natural to base the development of CAMOS on already exiting computers and interface to existing sonars.