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Down and Side Imaging

jeffcpr | Published thu Dec 07, 2017 8:16 am

Down imaging vs. Side imaging


Down imaging and side imaging are two newer technologies in fish finding that give a completely different and much more life-like picture of the underwater world.

The both use high-frequency SONAR waves to give a very detailed picture. Normal transducers operate at 50/83/200 kHz, but down imaging and side imaging transducers operate much higher, at 455 or 800 kHz.


Humminbird calls their technology Down Imaging and Side Imaging, Lowrance calls theirs DownScan, SideScan, and StructureScan, and Garmin calls theirs DownVu. All of these are essentially the same technology.

Some fish finders such as the Lowrance Elite HDI series and the Lowrance Hook series are DownScan only, while some such as the Humminbird Helix 5 SI are Side Imaging only.

Those fish finders are quite reasonably priced, but if you wanted to go all out and get something that has both, then the Lowrance HDS is the way to go – but combined with StructureScan, those will set you back a couple of grand.

So before you invest in a fish finder, it’s important to decide which to go for.

Advantages of side imaging

Side imaging is incredibly powerful technology. Because the transducer is shooting out sound waves on both sides of your boat, you can cover a LOT more water with side imaging than you could with down imaging.

A couple of runs up and down the lake and you’d have the entire area mapped out – you would know exactly where the good cover and structure is, and you’d also know the way the bottom is contoured.

Since 3D SONAR(another name for down imaging and side imaging) really shines when you use it to fish around cover and structure, side imaging gives you the best possible view.

With side imaging, you can also be sure of where the reading is exactly. In down imaging, if you see a bunch of trees, you won’t know which tree is where, since it is a flat image.

But with side imaging, you could see if certain trees were on the left and certain trees were on the right.

This was taken using down imaging. The trees seem to be in a line


The same area in side imaging shows you exactly where everything is

Advantages of down imaging

Down imaging comes in handy when you are examining a specific area of structure. On regular 2D SONAR, any large object will just show up as a blob of colors, varying in color depending on how soft or hard it is.

But with down imaging, you’ll be able to see almost exactly what it is – whether it’s a tree, a rock, a sunken boat, or just an underwater ridge, to name a few things.

Finally, down imaging is a little cheaper than side imaging. So if your budget is tight, something is definitely better than nothing, so go for down imaging at the least.

Down/Side imaging fish finders:

Lowrance Hook 5x – Down Imaging + regular SONAR

Garmin 151dv – Super cheap DownVu SONAR

Humminbird Helix 5 – Side Imaging + GPS


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