Terminology 101

Down Imaging, as the name suggests, is the ability on fish finders to provide detailed picture-like images of the bottom and structures directly below the Boat. The picture-like images are displayed using specific Down Imaging software that represents the returnSonar signal in a more realistic manner.

The term Down Imaging^TM is a registered trademark (TM). OtherFishfinder brands have similar software, but cannot refer to it as Down Imaging, eg. Lowrance have trademarked their software/technology as DownScan Imaging^TM (DSI).

The Frequency used for Down Imaging is typically 800 kHz (45°) and 455khz (75°) - hence the technology operates best in shallower waters. The 800khz Beam gives the sharpest image Resolution whereas the 455khz Beam gives the best overall image quality and depth.

When combined with Side Imaging technology, Down Imaging gives the user a full 180 degree view of the bottom. (c.f. Side Imaging, StructureScan)

Many marine electronic manufacturers will talk about maximum depths a Sounder should reach.

To our Way of thinking that is a bit like a cars speedo showing a maximum speed of say 250kph. That does not mean you will get that speed (unless you are travelling down hill with a very strong wind behind you!.)

There are many variables that affect the depth that a sounder can see the seabed.

These include:

• Amount of salinity in the water
• Thermoclines
• Beam Angle
• Transducer Frequency
• Output power
• Hull shape & Bubbles
• Type of Transducer - In Hull, Through Hull or Transom mounted

So when you see the term 'Usable Depth' this is a more realistic idea of what you can expect in most conditions - however there will always be an exception to the rule.