Earlier quoted context omitted.
Agreed. Circling surveillance planes are unsettling no matter if it is routine or not. I believe they should have warrants for these and maybe they do, maybe they don't. There is not enough transparency to know (even just a report of the number of investigations and outstanding warrants in cities or districts would be enough).
Why would they need warrants for watching a person in a public place? You don't have an expectation of privacy in that situation.
I think the similar argument here would be that a near constant observation of someone, even while in public, would amount to the same sort of search, even though one has a very low expectation of privacy while in public.