I wonder if the many Starlink satellites can be used for this? True, the signals are low and are steered, but the nature of steering creates many side lobes that will be useable in this manner. It would be a complex computational task with satellites in motion as well as ground stations transmitting on offset frequencies. I suspect various research/military labs are playing with this?
I did some searching and seems like an active area of research: https://ieeexplore.ieee.org/document/8768105/ and https://ieeexplore.ieee.org/document/9905046/
With their movement you might get some strange SAR like effects. Computationally complex but could add another dimension over a static tower.
Such radar would be a game changer.
Indeed, full spectrum Western dominance over air space in the global South could come to an end. If that goes, the chains of hegemony loosen significantly.
Indeed, a global game changer for politics, defense, environment, climate, a step towards world governance.
Imagine a large number of crowdsourced software defined radio receivers with FPGA's and extremely accurate femto-second timing calibration connected to the internet spaced apart geographically and a distributed supercomputer to do all the realtime calculations. No single country or army would have this detector but everyone could use it for defense. Now imagine the resolution would be accurate enough for detecting planes, drones, birds, people, ground vehicles, ships, fish, insects, wind, tree leaves. We are close, we just need a cheap planetary deployment (like we had with SETI@home) and write better software. I imagine in 10 years we all have a detector, like we all have a smartphone or a router with a firewall. A passive radar in every building for spotting drones above our house and garden.