I'm planning on a project that will be able to detect a net floating underwater. I'm trying to figure out if it's even possible to use sonar to check if a shape is a loose grid, like a floating net would be. Even just to see if it's a big flat thing that isn't an animal or something, and to have it print something when it does. Is this beyond the hardware capabilities of an arduino? could I use four sonar sensors pointing at two slightly different places? It would also all have to work underwater so I don't even know if underwater sonar sensors are a thing for an arduino. Anyway, any help or advice would be much appreciated, I want to figure out if this is even viable.
Please do some research first. Then build a prototype. Then ask.
Your post vanished, but you may ask google for "sonar fishing net detection". The first link leads to https://www.westcoast.fisheries.noaa.gov/publications/protected_species/other/rockfish/using_sidescan_sonar_to_locate_derelict_fishing_nets.pdf and by reading that paper you could conclude that it's way above your head. Sorry.
Is this beyond the hardware capabilities of an arduino?
Yes. Underwater sonar devices require specialized, high voltage electronic drivers.