Imaging sonar - fish arcing

Imaging sonars, like the DIDSON, BlueView, Kongsberg Mesotech M3 and Blueprint Subsea Oculus systems record movie-like images.

Sv frames raw sonar data

Fish arcing

Figure 1: DIDSON data horizontal mount. An imaging sonar scanning across a river and skimming the river bed. Seven image frames are shown. Stationary features and fish are imaged. A fish near the 4.5m grid line swims across the beams. In several frames a fish-arc artifact artificially elongates the fish.

Proposed cause of fish arcing: "near-range and/or highly reflective targets often create an artifact in DIDSON images that has been referred to as “arcing” or cross-talk. It is some form of interference that results in strong targets being “smeared” out into adjacent beams. The hallmark of arcing is that it extends the target left and right within a very narrow range interval, i.e. an arc.'' (A. M. Mueller comment on the deprecated Hydroacoustics forum).

DIDSON river mount

Figure 2: Imaging sonar set up to look across a river.

To enhance fish echoes for multibeam target detection it is possible to subtract static background objects and apply image algorithms.

Other identified images:

See also

Examples of echogram interpretation
Sound Metrics notes