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.
Swap "GPS monitoring" for infrared, EMF, video, audio tracking, whatever those planes are doing, and I think we are at the same level of "impinge(ment) on expectations of privacy."
Is it your opinion that Alito and Sotomayor are barking up the wrong tree? Is this sort of extensive (i.e. multi-modal (visual, EMF, etc.)), and evidently prolonged, monitoring not an impingement on typical expectation of privacy? Sure, this isn't a trespass, but if a private person was doing this to you, wouldn't you want to call the cops? (Oh, wait...)
In my opinion, the whole "expectation of privacy" thing is reading words into the 4th amendment that aren't there. If you look at the phrasing of the text, which focuses on "searches" and "seizures" of "persons, houses, papers, and effects" it's clear that the 4th amendment prohibits the government from doing what would be a common law trespass (to the person, to real property, or to chattels). It's based on property rights, not privacy.
If you are following someone in the matter the police would they won't know they are being followed, which is part of what private investigators do.
Just don't harass them. If they catch you and tell you to stop and you don't - then you are veering into harassment territory.
That's because it would be stalking.