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Suppose you were fishing 40' water and had SI range set at 35'.. what would you see (if anything and how would you interpret the returns??? Now if you changed settings to contour mode, would you see anything different or have a different interpretation?
May have to try this next outing, just out of curiosity.
You will only see the dark water column...
35' SI Range means the unit will only display return echoes from within that 35' distance away from the xducer...
In your scenario of 35' SI Range...If you took a 35' rope and attached one end to the xducer...and then swing that rope in a semi-circle from 35' horizontal right to 35' horizontal left...every echo within that semi- circle would show on the display...(within the upper reaches of the selected SI beam frequency)...
Every echo outside of that semi-circle would not be shown on the display...
Setting the HB SI Contour mode to "On" would show a blank screen with no echoes anywhere because you told the unit not to show echoes closer than 35' Range with the Contour Mode setting...in addition to setting the SI Range setting at 35' told the unit not to display echoes farther than 35' Range...
http://i477.photobucket.com/albums/r...psm7jtyyhn.jpg
Rickie
Thanks, Rickie....... so if you had range set ~5ft over depth, would you have a 10' width of down imaging in contour mode?
As the Range setting in SI is attributed to "Slant Range" instead of "horizontal distance"...the amount of bottom showing will be less than 5' each side ...(in your scenario of 5' SI Range greater than depth)...Quote:
Originally Posted by cache22
Robert explains "Slant Range" here....
Slant Range vs Horizontal Range and Calculating Waypoints
But your basic thought is still correct....(if I'm understanding your scenario correctly)...
*You can set the SI Range greater than the depth (5' SI Range in this instance)...
*This will show a "less than 5' section" of the bottom detail on each side of the "dark water column"...
= Then setting "Contour Mode" to "On" will eliminate the "dark water column"....and, in effect, stretch (horizontally only- not vertically) ....the remaining data on the screen towards the center line...(probably into something unrecognizable because the vertical data did not change)...
(Kinda like buttoning a shirt that's too small...will "stretch" the material towards the center...but the shirt didn't get any longer)...
Rickie
Does this mean that contour mode distorts (stretches) the side image when range is set wider?
In effect, Contour Mode is going to "stretch" the bottom detail showing on the display ...to a degree depending on the ratio of "dark water column to SI Range setting" ...showing on the display...Quote:
Originally Posted by cache22
If the dark water column takes up a lot of the display...removing that dark water column (with Contour Mode On) will "stretch" the remaining bottom detail a lot more than if there were less "dark water column" and more bottom detail showing...
Here are 2 "Contour Mode On" examples..(extreme examples for clarity)...
*Water depth of 10' - SI Range 100'....the "Dark water column to SI Range ratio" is small = less horizontal bottom detail distortion...(with Contour Mode On)...
*Water depth of 90' - SI Range 100'....the "Dark water column to SI Range ratio" is large = more horizontal bottom detail distortion..(with Contour Mode On)...
This is because "Contour Mode On" is telling the unit to display the same amount of bottom detail currently showing on the display ...and stretch it horizontally over more of the screen real estate...
Now, importantly, that's the way it works in my head....I haven't actually tested this live on the water to see if my understanding is correct...
Rickie
Rickie,in roberts pic,when he change the contour mode,i counted the lines on right side and counted 20 to dark spot and 8 on other side of dark spot,with contour other way ,only 4 lines after dark spot,it looks like it start in middle of each side and then stretch out leaving the middle of each side as center of the stretch?
This is the depiction in Robert's Slant Range tutorial...(is this the image you refer to Gene?)...
http://i477.photobucket.com/albums/r...psd0qkwj9h.jpg
And here's a partial clip from Robert's tutorial...
The records below show a portion of sonar image before and after correction for slant range and speed distortions. Note that the feature closer to the sonar is changed more by the correction process than the features further away.
I think the important thing to take from this is that the SI image (Contour Mode On or Contour Mode Off) may not be a "true" representation of actual linear distances across the lake bottom....
This is because the xducer is always above the bottom (dictated by depth)...and because the unit may be applying "correction factors" (proprietary that only the brand knows)...
This is why waypoints marked on the SI image should always be verified (and remarked) with inspection from the "down pointing" 2d cones ...
Rickie
Starting to make sense to me ...... thanks, Guys? Since it is rather difficult to pick up fish returns in contour mode, I think I shall leave it off.
There's an interesting story that goes along with this thought...Quote:
Originally Posted by cache22
Back before there was Contour Mode...one of the most often requested wish list items on the forums was to be able to turn off the dark water column...
Several years guys asked for this feature...
HB finally instituted Contour Mode in 2011 (or 2012 I'm not sure)...as a feature update software...
Very few even use it ...even after all the calls for it in years past...
I think guys realized that there is valuable information in the dark water column....
I only use it when someone has questions about it or it's use in imaging...
Rickie
Ricky,Quote:
Originally Posted by rnvinc
Does the HB have a depression angle on SI or does it pick up surface clutter.
Explain "depression angle"...I haven't heard this term before...Quote:
Originally Posted by larryb227
Rickie
The angle produced by the surface of the water and the edge of the side scan beam from the side scan ducer.Quote:
Originally Posted by rnvinc
(I tried to add a PNG drawing but the site hangs up and I've had to start over several times. It freezes when I try to change the size of the thumbnail)
It is usually done to avoid the surface clutter.
It would be my guess (and maybe Greg can shed light here)...that the SI image processing has a filter (similar to Surface Clutter under the Sonar tab) to help with any near field reflective targets in the area of close proximity of the SI piezoes...Quote:
Originally Posted by larryb227
Each filter in the unit (Surface Clutter, Noise Rejection, Switchfire, Fish ID, etc)...has it's own specific algorithm criteria that it "filters" out of the displayed image...(the echo data received is "the echo data received" ....each specific filter {working within its own criteria} ...just says "Nope- not gonna show that echo, and not gonna show this echo" ...and so on)...
If there is a filter specifically for near field clutter in the SI image processing... it's not available to users because I think the present "Surface Clutter" setting under the Sonar tab only affects the 2d image processing...
Rickie
Ok Rickie if that is how the HB works.
Generally surface clutter is from 0 depth to half the depth the unit is set at with the attenuation gradually coming back to full sensitivity. (mostly on 2D sonar) In SI your surface clutter is present to the end of your range. Near field in not the only problem.
Basically you are saying the beam is not depressed.
I agree the near field is not the only problem (because the beam form is going to be in this area of possible surface clutter for a greater distance than a "down pointing" beam form)...
And from the "calculated" beam form depiction (see below)...I can't see where there is any measured "depression angle"...because the sound pulse (in both frequencies)...reaches all the way to the water's surface...albeit at "ever-decreasing pulse strength"...
The echoes are there (if the beam form is there)...the processor (and/or it's associated filters)...decides which of the total echoes are painted into the SI image..
http://i477.photobucket.com/albums/r...pshmz3szda.jpg
I'm only guessing that there is a specific filter used for omitting "surface clutter" type echoes in the processing of the SI image...(there is no setting for SI surface clutter...but that doesn't mean one doesn't exist...we just don't have access to it)...
Maybe I'm mis-understanding your meaning of "depression angle" (as relating to an SI image)...(or it's delving into an area of sonar technical data I have yet to learn)...
Because in SI sound pulses thru water ...there is no measured angle (that I know of)...from the water's surface to the "edge" of the SI beam...
There is no "edge" in any sound pulse beam form...only the brand's own criteria for how they measure the "ever-decreasing strength" of the sound pulse before it reaches 0db ...or "Absolute Silence"...
And of course there is the measured angle at 0db "Absolute Silence"...but that angle is way out past the "advertised beam angle"...(brands have no need in advertising this 0db angle...so we never see it in advertising)...
Rickie
I found this ...that speaks of "Depression Angle" as applied to sonar...
NAVAL SONAR - APPENDIX - DEFINITIONS
I have no idea if this relates to any Sonar Beam form scenarios that are fixed direction "side pointing"...
Rickie
I've always understood that the depression angle I'm talking about is of course, theory. Side lobes will change much of that but the dicer is cut to have a certain angle i.e. 30 degrees or 20 degrees or what ever. In side imaging the beam is very narrow like a pencil beam therefore helping the resolution along with frequency.Quote:
Originally Posted by rnvinc
Bottom line I'm sorry I mentioned it.
Heavens no ...don't be sorry about mentioning anything here...we learn by discussion...and your topic has me motivated to study more about "Deflection Angle"...Quote:
Originally Posted by larryb227
I like learning..
I will mention ...you are absolutely correct that piezoes are formed to a specific size and shape to achieve the desired beam angle (and beam shape)...that each brand desires for their specific sonar beams....
http://www.marinop.it/pdf_doc/Transducer%20Design.pdf
http://www.airmartechnology.com/uplo...Operations.pdf
But how the brands "measure" that beam angle ...compared to "cartoon depictions" of brand's advertised beam angle is misleading (to say the least)...
The sound pulse doesn't just go to the edge of the depiction beam line and stop (as it seems in the depiction below)...the sound pulse continues past the "measured beam angle" in an ever-decreasing strength until 0db....no sound....
http://i477.photobucket.com/albums/r.../HB/unjpeg.jpg
This very topic of the advertised SI beam angles was 1 of the most difficult discussions to hash out when HB SI hit the market...
That the "cartoon depictions" of the individual left and right SI ...did not touch at the bottom of the HB depiction...(see depiction above)...
It was discussed for months before it was understood that there was no gap in coverage of the SI beams...but just the way HB measured the "advertised beam angle" ...and their assigned measurement numbers didn't add up to ...no gap...
Here is some of that initial discussion and testing that proved the SI beam angles depicted in the HB SI advertisement were merely "measurements" ...and not where the sound pulse actually stops...
The Proof of Humminbird Down Imaging
It wasn't until much later that Rickard and some of the other wave theory experts at sideimagingsoft dissected the HDSI xducer and calculated the mathematical beam forms to show just how far past the "advertised beam angle" that the sound pulse actually travels ...
Rickie
Most of the industry in the beginning used 3db point to make these beam measurements but as time went on they got larger cone angles by stated what the 10db points were. (nothing really changed) For me most of this is not for the average fisherman and I've always tried to explain using our every day approach. If you are in design of xducers fine or just interested in the subject that's fine. I know that the graphic example is really for explanation only and of coarse sound continues until it fully dissipates. (0db)
Information overload, lol. Im trying to learn all this, but now my head hurts. Ricky is there some sort of literature that I can read that has a definite starting point and a ending point. Ending point being I know everything there is to know about these things. Im reading my owners manual, but what reading im not getting it all mostly because im not looking/scrolling thru my unit at the same time. Confusing. lol
Read this about Sonar history...Quote:
Originally Posted by LowePro
Sonar - Wikipedia, the free encyclopedia
Then read this about how piezoes are made and how they work...
http://www.airmartechnology.com/uplo...Operations.pdf
Then read this (kinda skim over the mathematic equation stuff and read the rest)..
http://www.marinop.it/pdf_doc/Transducer%20Design.pdf
Then read this about Side Scan Sonar history...
Side-scan sonar - Wikipedia, the free encyclopedia
Once you understand how (and why) Sonar came about...
And then have a basic understanding of how piezoes perform the following 2 functions...:
*Change electrical energy (signal)...into mechanical energy (vibration) =......this is the transmit (ping)..
*Change the received echo (vibration) ...into the returned electrical energy (signal) =this is the return echo data...
Then most everything else is just learning the different features that each brand puts into their products...
Rickie
Great info Rickie
Thanks