Thread: A Questioning Mind

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...



Rickie

Originally Posted by rnvinc

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...



Rickie

Ricky,
Does the HB have a depression angle on SI or does it pick up surface clutter.

Originally Posted by larryb227

Ricky,
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...

Rickie

Originally Posted by rnvinc

Explain "depression angle"...I haven't heard this term before...

Rickie

The angle produced by the surface of the water and the edge of the side scan beam from the side scan ducer.
(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.

Originally Posted by larryb227

The angle produced by the surface of the water and the edge of the side scan beam from the side scan ducer.
(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...

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.

Thanks, Rickie....... so if you had range set ~5ft over depth, would you have a 10' width of down imaging in contour mode?

Originally Posted by cache22

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)...

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?