A possible object identified in sonar data and logged with a number, position, dimensions and an image. Side-scan contacts are measured from their shadows, correlated between overlapping lines and compared with multibeam, then classed as significant, insignificant or false. Significant contacts are developed for least depth; a contact seen on only one line with no shadow is usually written off as noise.
Contact 27 shows on both lines with a 1.5 metre shadow, flag it for development.
Correlate a contact on at least two lines before spending boat time on development; single-line contacts are often fish, weed or noise.
Also heard as
- target
- sonar contact
Related terms
Side-scan sonar
A sonar that images the seabed to either side of its track, revealing objects and textures by their echoes and shadows.
Acoustic shadow
The dark area behind an object in a side-scan image where the object blocked sound from reaching the seabed.
Development
Extra survey work over a feature or shoal to pin down its least depth, shape and extent.
Feature detection
The ability of a survey system to find seabed objects of a stated minimum size, usually given as a cube edge length.