Here is a quick and dirty way to remove/lessen the nodes (the dark areas next to the water column) in ur side scan data, making the image much clearer. Basically, what we will do is to make the DOWN SCAN DATA channel switchable (ON/OFF) - which will enable us to use the LSS2 as we normally do (side scan and down scan) or use the side scan data only, while keeping the down-scan depth info alive. This will remove any down-scan signals in the water, making the nodes disappear/lessen, resulting in much more detail in the SI data. Another plus of this mod is a higher penetration depth in muddy/light sand bottoms - resulting in buried objects showing up on the side scan data.

Here is the rundown:
Take your cable or extension cable and place it in front of you with the plug towards you and the length of the cable running away from you.
Take a very sharp knife, better a surgical blade such as seen in the picture and cut a small section of the cable insulation away. Make sure you only cut the insulation and nothing inside the cable.
Peel off the insulation.
Find the GRAY & BLACK single wires. the silver-wrapped pair in between those two singles is our down-scan channel.
Carefully cut the silver shielding of that pair and cut the yellow wire inside right in the middle.
Pull out both ends, take about 1mm of insulation off and solder a toggle-switch in line.
Insulate all the exposed areas of the cable well and make sure to restore the shielding as best as you can - so no gain-loss will occur. Ideally, try to shield the switch as well. I use air-con aluminum tape & tin foil.
Now make sure you tape the switch nicely in place - I use self-amalgamating tape for this. Be generous!
Lastly, a layer of marine-grade insulation tape to keep everything sealed and waterproof.
Done aaaaand done.
Enjoy your new and improved side-scan images.

Last two pix... :)

I have found that tracks created like this have some issues with the gain and slant range (I think) in RM. Its great for work on site where a consistent image is required, but doesnt get good results with RM mosaic. Maybe Matt can elaborate on the likely effect of no DS data on the mosaic ?

T

So, what does it all translate to (in the real world)???
Here you go - some fresh images, right out of REEFMASTER.
Notice the pronounced detail of stuff when the DI channel is off (darker images/areas).
It's quite self-explanatory.
This works BEST within the first 20 meters!!! Ideally in 10 meters of water.

I'd be really interested if you could point me towards a few tracks that don't have DS, or send me some. If the recorded image is good then the only thing I can think of that would affect things is poor bottom lock. Perhaps that can be an issue? Inaccurate depths also play havoc with the autogain.

JK4U wrote:
Nice pics! Really interesting, thanks for posting. Interesting to see that there is still some DS return even when "off".

AnglingCharts wrote:
The funny thing is that there IS down-imaging data! At least in my scans - when the DI channel is switched off, the attenuation drops by probably 60-70db. However, there is still some data - which must be picked up from scattered reflections from the SI channels. I am not sure where it comes from, but u can see on the screenshots I posted that it is there. :O
I can confirm your observation regarding the loss of gain and loss of reach. Even upping the contrast will not restore the image. Same is happening on the HDS while in use.
Why do you think this is?

Interesting!
will try on my ONIX , can do on/off from the unit and look to the diffrence by using differentes frequencies for DI and side !