My radar is quite low, on the stern. I can pick up the Walton channel buoys fairly easily but haven’t tried it in anger. I don’t think the resolution matters very much at the nearest range setting. I think that I have only once entered the Backwaters from out to sea in the dark and I remember that I found it surprisingly difficult, even with a plotter.There have been debates about these before, but I think they'd be ineffective. They work on infrared so essentially they pick up differences in temperature. Good for seeing a live body in the water, but a buoy at the same temperature as the water round it wouldn't have much contrast. The other point is that for physical reasons, the resolution of infrared sensors is less than that of optical devices, so the picture is inevitably blurry.
People with military experience have spoken of light amplifying devices (photomultipliers and the like) but the cost of useful kit puts it out of reach for us!
Radar would work for the yachts moored in the Walton channel, but it's relatively low resolution and of course, there's a minimum range within which you get no returns. I've just had one fitted, but I'm not ready to trust it for that kind of navigation!