This may be off topic but I was an engineer working in Pasadena, when the local paper broke the story on the seismic tracking of flying objects returning from the Pacific range. I believe it was a real story and caught the operators of whatever it was off guard. The story disappeared instantly IIRC. To me, the items important in that story were as follows. 1- the seismograph system in southern California could track flying objects in 3D. 2-Each object of different configuration generated a unique signature. 3-The system could give approximate dimensional values. 4-The system could give approximate gross weight values.
So there is a stealth proof system for tracking and identifying pretty secure from any sort of "spoofing". Could this concept have been developed into a space dropped system of micro-seismographs into suspicious areas that could give early intel warnings of developing, and using any type of aerial system?
ArtieBob