Down Imaging versus Side Imaging

Doug Vahrenberg · Post by **Doug Vahrenberg** » Wed Oct 05, 2011 6:11 pm

I get asked many times about which is better. To me Down Imaging with it's limited coverage area is less attractive than Side Imaging...One reason: Coverage Area. And most importantly Coverage Area away from the boat.

Down Imaging has benefits and is a great step to transition from Traditional 2D Sonar to High Frequency Sonar but both 2D Sonar and Down Imaging lack the coverage area of Side Imaging.

2D - 200kHz Sonar is 20 Degrees or 1/3 of Depth
2D - 83kHz Sonar is 60 Degrees of about equal to Depth

DI has different coverage. DI from SI has three user adjustable widths: Narrow, Medium and Wide.

Narrow is close to the 200kHz or 1/3 of Depth
Medium is close to the 83kHz or Equal to Depth
Wide is wider than both and close to 1.5 times the Depth.

In Down Imaging/2D models the coverage area varies by frequency:
800kHz is approximately equal to Depth
455kHz is approximately 1.5 times the Depth.

With Side Imaging the user selects the amount of Area of Coverage in the Menu. So you can view how much bottom and to the side coverage out to 240' to each side for a total of 480' of coverage...no matter the depth. This is the power of Side Imaging.

Here are a couple examples of the exact same structure showing the additional data that DI does not provide.

Down Imaging:

Side Imaging:

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But Can DI tell you Direction? Just like 2D sonar you cannot tell which side of the transducer the data came from...

But Side Imaging I can tell which side of the transducer the data comes from...

This image is marked up to show where SI shows the blocks versus DI that has no ability to tell which side

Hope this helps understand the features and advantages and the differences.

mark poulson · Post by **mark poulson** » Sat Nov 12, 2011 8:24 am

Doug,
I fish clear SoCal lakes.
What sensitivy do you recommend for SI and DI?

Doug Vahrenberg · Post by **Doug Vahrenberg** » Sun Nov 13, 2011 5:34 pm

Start SI on 10 and DI on 12 then ajust as needed. My SI range is normal 8-12 and DI is 10-14 for sensitivity. Water Color has no effect it's adjusting to get the data you need and more a contrast control.