SUPPORT > SIDE SCAN IMAGERY > REFLECTED TARGET INTENSITY

To complete our understanding of the basics of sonar imagery, we need to consider the brightness information (intensity of echo) shown on the sonar display. As with a surface reflecting light, different surface textures and materials of targets have different acoustic reflective properties. Typically the more the density of the target differs from that of water, or the more rigid its material is, the more sound is reflected back.

• Any target with a gas in (such as air) will act as an almost perfect reflector for sound, and will show as the brightest colour in the palette.
• Muddy or silted lake and sea beds will generally show up as a low-intensity background colour, as mud is a good sound absorber and contains water.

The example sonar image below shows several bright targets of interest...

Taking what we already know about sonar imagery into account we can interpret the following...

• White 'dots', without any form of shadow are most likely either flat hard targets on the bottom or large mid-water fish (with their air-filled swim-bladder showing up on the sonar).
• At the bottom of the image we can see a bait-ball of fish - identifiable as large spherical structure that protrudes above the seabed profile (there is a faint and fragmented shadow extending away from it, implying it is not a single solid target).
• On the right of the image, we can see several vertical curved white lines. These are most likely the hulls of moored boats, and close to them we can see the square outlines of the concrete mooring blocks.
• At the top of the image, there is a large target. As it appears on both channels, and we can see its profile, we know the sonar has passed directly over it. The bright geometric echoes on it indicate it is probably man-made, and there is an acoustic shadow visible on the right portion of it, showing it has height. It is most likely this is the wreck of a sunken vessel.