I'm not so sure. With the latest electro-optical turrets a helicopter can be pretty far away and still get usable footage. During the Football World Cup I observed some police helicopters orbiting just about out of earshot during their operations.
I've also seen a demonstration of an experimental locally-produced surveillance camera (in this case intended for maritime observation) that was able to display the name on a small boat 20-30km out to sea. Granted, the camera was mounted on the top of a mountain to get the required height, but nonetheless the technology was phenomenal.
The difference between all the different varieties of surveillance technologies is starting to blur quite a bit.
There's a huge difference in price, though. The numbers will probably work out that you can throw up a hundred or so drones for the price of a single helicopter. With a single expensive platform, expensive optics and highly trained operators make sense.
I've also seen a demonstration of an experimental locally-produced surveillance camera (in this case intended for maritime observation) that was able to display the name on a small boat 20-30km out to sea. Granted, the camera was mounted on the top of a mountain to get the required height, but nonetheless the technology was phenomenal.
The difference between all the different varieties of surveillance technologies is starting to blur quite a bit.