A while ago I was looking at buying a LS 410 mono sounder only to find that the specs had a minimum depth of 2m. Did speak to the agent who confirmed that signal degrades significantly in depths under 2m.
Given that the majority of fishing that I do is under 10m and a lot in under 2m which of the current crop of sounders would give a decent image at under this depth.
Most give a maximum depth but not minimum.