Hot Air Balloons
Watchman radar picks them up close ish in, say 15 miles . I had one last year and asked him to set QFE and report his height..........eh minus 50ft! My airport on a 500ft hill!
Radar can pick up all sorts, last week I was flying and ATC called traffic right to left 2 nm no height. It was I think the 1415 Cardiff to Paddington GWR train! Up in northern Scotland in the Moray Firth have had oil rigs called to me. Though of course in ATC we have to call any contact.
NM