Down Imaging versus Side Imaging

[Doug Vahrenberg]

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.

[Doug Vahrenberg]

I was questioned on another forum about the first images and where the data was in the Down Imaging compared to the Side Imaging so I marked them to show reference and the added coverage you get to the sides with side imaging. Hope it helps...

[T Mike]

outstanding illustration Doug. No Doubt SI is where it's at.. to me DI is just training wheels for reading your sonar which isn't a bad thing.

[jdb21867]

Great explainations---but I really have to study them to to "get it". Experience is a huge part of those who can quickly decipher what they are seeing.

[Doug Vahrenberg]

That's why we are sharing information to make it easier for all to learn. Nothing beats time on the water and experience but the learning curve is accelerated with reviewing these images...