The US Military will conduct high altitude MESH networking radar tests over South Dakota to provide a persistent surveillance system to locate and deter narcotic trafficking and homeland security threats.
High altitude balloons will fly at twice the altitude of passenger jets and use radar to simultaneously track many individual vehicles day or night, through any kind of weather.
Interferometric synthetic aperture radar is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface deformation or digital elevation, using differences in the phase of the waves returning to the satellite or aircraft. The technique can potentially measure millimeter-scale changes in deformation over spans of days to years.
Synthetic aperture radar placed 20 times farther away than the militaries high altitude balloons can scan for features at 30 centimeters (one foot or less). Synthetic aperture radar from balloons would likely be able to create 3D surface images with one-centimeter accuracy. The balloons would be able to update several times a minute.
Simple high-resolution optical cameras were already used in Iraq, Afghanistan and Dayton, Ohio to monitor the movement of all people and vehicles. About ten years ago in Dayton a Cessna flew for everyday for weeks and created video that could be used to Tivo all movement. When murdered bodies were found they were able to rewind and find the house where the murderer lived. They were able to solve 75 murders over the period of the monitoring.
The technology for this monitoring is trivial. The radar monitoring can see through buildings and any other obstruction.
Dayton monitoring from about ten years ago
Not Shield Helicarriers But High Altitude Balloons
In the recent movie Captain America Winters Soldier there was a debate about this surveillance between Captain America and Nick Fury.
Hydra-Shield Monitoring from Helicarrier in fictional Winter’s Soldier Movie