Automated surveillance – the ability to reliably detect people and vehicles from a camera – is getting very good. The measure most often used is probability of detection vs false alarm rate (a receiver-operator characteristic curve (ROC)). The likelihood of detection is in the very high 90s, and the rate of failure equivalent to fewer than one a week for continuous operation. You can thank DARPA (again), as the VSAM project is largely responsible.
This is the good news: a virtual fence will work as advertised.
The bad news: a virtual fence is useless without a real fence or significant personnel. Why? Think about the situation at, say, the southern US border with Mexico. You can get omni-directional camera towers every 100 yards. Nothing gets through without detection. A computer alerts you to a few dozen people ambling across the border.
Then what? They walk unimpeded because there is no fence. They are not stopped by any kind of border enforcement, because those folks simply don’t exist in the numbers needed to guard a border thousands of miles long.
A real fence makes it so that far fewer people try to cross. A virtual fence makes it so the few personnel you have are much, much better utilized.
I can only conclude that politicians that push for a virtual fence in place of a real fence with adequate man-power either don’t know what they are talking about, or want the effort to fail.
I would prefer they just let the experts handle the situation, and subsidize the effort with thousands of iRobot’s latest, greatest robot: Warrior.
p.s. I can build a unit today that can see 100m reliably in any direction for less than $20K. The 3141km border can be doubly covered with 31k of these towers. That’s less than $1B. The US defense budget is $466B a year. Sad, isn’t it?