DFF3D ISSUE: The inconsistency between the multibeam and water column history fish target display

[hillman]

See the screenshots below, fish school image marked with circles on multibeam sonar screen and water column history, They are the same school of fish, but why do they appear as one or two fish on the multibeam screen, but appear as many small bubbles stacked together in the water column history? Is the display logic of the water column history that one bubble represents one fish? Thanks for any reply!

 

[Johnny Electron]

@Deep Blue

 

[jp498]

It seems to be adjustable in Timezero; have you played with these in Options/Multibeam :

• Water Column (with DFF3D)​

  • Fish Detection Level: Adjust the sensitivity of the Fish Target ("bubbles") displayed on the Water Column display. If you have too many fish targets that clutter the screen, you can decrease the sensitivity by selecting "Low". If you feel you do not have enough fish target displayed on screen and would like to increase the sensitivity, adjust this settings to "high".
  • Seabed Echo Calibration: If school of fish located at the bottom are not detected as Fish Target (Bubbles) and are instead inaccurately detected as bottom and create bump (fake rock) in the depth recording (PBG), you can increase this setting. On the opposite, if rocks at the bottom are detected as fishes, decrease this settings to remove fake fish target detection at the bottom.

 

[hillman]

It seems to be adjustable in Timezero; have you played with these in Options/Multibeam :

• Water Column (with DFF3D)​

  • Fish Detection Level: Adjust the sensitivity of the Fish Target ("bubbles") displayed on the Water Column display. If you have too many fish targets that clutter the screen, you can decrease the sensitivity by selecting "Low". If you feel you do not have enough fish target displayed on screen and would like to increase the sensitivity, adjust this settings to "high".
  • Seabed Echo Calibration: If school of fish located at the bottom are not detected as Fish Target (Bubbles) and are instead inaccurately detected as bottom and create bump (fake rock) in the depth recording (PBG), you can increase this setting. On the opposite, if rocks at the bottom are detected as fishes, decrease this settings to remove fake fish target detection at the bottom.

I appreciate you explaining that. I use the default settings. But it looks like one fish in multibeam display, it's actually a school of fish in water column history.
My question is, in addition to accurately showing the exact location of the fish, does the water column history display also accurately show the size of the fish school, which the multibeam display cannot do?

 

[jp498]

Most of my experience with DFF3d and sounders in general is for bottom mapping and understanding underwater habitat. Only recently (past couple of years) have I used them to view fish. I don't think the 3d water column presentation is a high detail presentation. I would arrange the screen to be split or have multiple screens to watch the triple sounder view, the 3d water column view, and section view. Each view provides useful data, that work together the provide a better understanding of what's down there, even if they don't all perfectly agree mathmaticly.

Also if there are multiple fish in the same depth, they may show up as one fish because of the echo timing as the boat goes by only sampling some of the water. If you are still you may find fish of the same depth moving to the side and be more evident in the triple sounder view or section view.

 

[hillman]

Most of my experience with DFF3d and sounders in general is for bottom mapping and understanding underwater habitat. Only recently (past couple of years) have I used them to view fish. I don't think the 3d water column presentation is a high detail presentation. I would arrange the screen to be split or have multiple screens to watch the triple sounder view, the 3d water column view, and section view. Each view provides useful data, that work together the provide a better understanding of what's down there, even if they don't all perfectly agree mathmaticly.

Also if there are multiple fish in the same depth, they may show up as one fish because of the echo timing as the boat goes by only sampling some of the water. If you are still you may find fish of the same depth moving to the side and be more evident in the triple sounder view or section view.

So what do you think of the case in my screenshot? The one or two fish I circled on the multibeam screen, and there are more than a dozen fish in the same position in the water column history display。
My understanding is that the water column history shows the specific shape and number of this fish school, while the multibeam display cannot do this.