HoW enviromental differences affect sonar images...(especially SI images)..

[rnvinc]

Here are 2 SI images with similar unit settings but giving stark image differences......

Differences that can only be attributed to enviromental differences in the 2 areas the images were taken..... Water depth/water clarity/bottom hardness....

Both images were taken:
1. Same 800 kHz beam setting
2. Same approximate boat speed
3. Same chart speed
4. Same "Contrast" setting 10
5. Same "Noise Filter" setting off
6. Very similar "SI Range" left and right

*One image very clearly shows the bottom all the way to the 90ft "SI Range"...hard bottom/clearer water gives better reflections for the sonar ping data to return to the unit...
*One image starts getting dark at 25-30ft out from the centerline...soft bottom/murkier water does not give as good of reflections for the sonar ping data to return to the unit...

It is my hope to shed some light on why some images just turn out better than others.....

Sometimes .....There are enviromental differences in the underwater world that just affect the sonar reflection echos differently....

Rickie

[crappiemax]

Thanks for posting. Makes sense to me.

One thing I noticed is even though side scan is similar, the water depth does seem to be different.
The upper pic seems to be much deeper also why pic seems clearer farther out.
The lower pic looks to be shallower water, hence side scan is less effective at those farther distances.

I generally keep mine at 3x -4x water depth for best pics (HDS). I'm new at this so I'm no expert.
Just sayin'

[Stymie]

Just noticed you moved this to its own thread. Good idea, I'll leave the other alone. A copy of my last post.


Found this from another thread.

"Navico (Lowrance) provides the following guidelines on the limitations of side and down scan coverage:

In 20' of water using 800 kHz the maximum capability of the HDS system is 35' per side. Couple that with 20' downscan coverage and you can view a 90' window. No reason to set the side range any higher because the system is not capable with those settings. 455 kHz will increase distance at the expense of resolution per the chart. Humminbird specs are very similar.

Compared to conventional sonar, 90' is pretty good though. A 200 kHz (20 deg cone) freshwater transducer would show 1/3 of the bottom depth or roughly 7'. The 83 kHz would display double that or 14'. 90' of coverage vs. 7'...this is why bigger screens are important for side scan imaging."

I do find the HB statement odd, as that's not the case as seen from these posts. BBC Boards: Humminbird SI Screen Captures from 0' to 10'. Scrool down to the 7th post. Those kind of images get my interest when I'm fishing.
If I followed Navionics advice, I'd have my SI set at 8 feet and would miss that big school of fish.

[mduncan62]

Based on what Stymie said, I'm barely able to use my HDS unit. It just doesn't do what the HB units do. I used to have an HB unit like stymie's, and I'd see a big school of fish 300ft away and mark a waypoint, and then I'd spend an hour trying to find it, only to realize that the school of fish had moved, and the darn donut made me run in circles.

Then I found this

and this is possible

Just seems like if you are going to make statements, they should be truthful, and based on fact. I do, it's easy.

[mduncan62]

Again, to back up Stymie, you can barely see the scuba diver here. HDS just doesn't stack up. And you can see how much better 2D sonar is at showing what structure really is!!!!

[Stymie]

I'm sorry that you don't know how to see somthin on the right of your screen, find a landmark and go towards it, come on down here and I'll show you how its done.

I like that DI image though. I can see why you use it for your style of fishin. And from the looks of that Si image, I can see why Si doesn't work out for you.

[mduncan62]

Don't feel to sorry for me, my GPS works as expected. What if you can't see a landmark, and have to depend on your electronics? I guess it's give up time and go home? That's when I find something that works. Lowrance HDS gets me on the spot, without running in circles.

[Stymie]

If I see a bunch of white specks on the right side of my SI, I don't need a GPS to help me turn right. I don't need a directional arrow to tell me that I turned right.

Different styles of fishing. You are looking for a pile to sit on and like to go slow. I'm hunting active fish and moving. Nothing wrong with either method, they both put fish in the boat.

I like that green image above. Finally seeing something 80 feet out. You got any 80 feet out in 5 feet of water?

[rnvinc]

Just noticed you moved this to its own thread. Good idea, I'll leave the other alone.

Sometimes when I find (or think of) information that others would find useful...I start a new thread with that information...

Not only does it allow a new discussion... It also makes it easier to find using the "Search" function of the forum...

New info (that some one may want to find or refer to) brought out into the middle of another thread is difficult to find later...if need be...

My goal is to provide the new information that helps users understand some of the variables involved in "why does this image not look like that image"....

One of the most common asked questions from SI users is ...
"What settings do I use to get images like I see on the forums?...

Sometimes it's not the unit's settings... Sometimes it's the enviromental differences that need to be taken into account...

Rickie

[tommyboyrn]

Rickie, Im still learning and this stuff is great!!!! Many thanks!