TESTING DISCUSSION WORKFLOW: Erik's Horns (Railroad Tracks)

[kjerram]

This is a test of the proposed workflow for adding a topic first under the Discussions, then moving the condensed and clarified answer from that content to the Troubleshooting page.

It's possible these should go under Issues instead of Discussions, but let's test this first.

[kjerram]

From the EM / SIS Troubleshooting Notes:

(EX2101, SIS v5.6.0.441) In acoustically soft sediments, lower-frequency systems like the EM304 and EM124 may suffer from a bottom detection artifact near nadir known as ‘Erik’s Horns’ or ‘railroad tracks’ because of the appearance in the grid. (Images show up a little differently after conversion from Slides to PPTX, but oh well.)

[kjerram]

"Hey, we see that too!" - deepwater mappers all over

[kjerram]

Carrying on with a little more context... Again, from the EM/SIS notes and EX2101 report:

The system appears to be detecting high-amplitude returns from the specular reflection (i.e., near-nadir seafloor that is directly facing the echosounder) and tracking this return on RX sidelobes at a fairly constant range (probably limited to within the TX pulse length) out to several degrees on port and starboard. The Penetration Filter may compound this artifact by encouraging the bottom detection process to select shallower candidates for each RX beam near nadir, such that the reported bottom detections follow the constant-range trend as it moves above the seabed out to several degrees on each side. Subsets below show Erik’s Horns (top) with normal runtime parameters (top) and after tilt and filter adjustments (bottom).

[kjerram]

That little spike at nadir seems much easier to filter / edit than the railroad tracks... and means more soundings that are representative of the seafloor. Yay.

[kjerram]

Proposed solution, again from the aforementioned notes and EX2101 report:

One method of reducing this artifact is to slightly reduce the nadir reflection strength by tilting the TX direction forward or aft by up to a few degrees. The highest-amplitude return is directed slightly away from the sonar, allowing the bottom detection process to more clearly/quickly distinguish between the seafloor (at the correct range for each RX beam main lobe) and the high amplitude of the first return (at a constant range across many RX beam sidelobes near nadir).

[kjerram]

Looks better. Now someone volunteers to condense this set of symptoms and solution on the Troubleshooting page.