Each of us has heard of the method of applying the ear to the tracks and listening to whether the train is going. You can hear the train at many kilometres. erstwhile there is simply a gap in the rail, the sound reflects and does not propagate. The plan of sound sensors spreading along the tracks is simply a task for students of the University of Technology. Nothing very complicated.
The theoretical bases are. For example, in specified a publication:
https://www.sciencedirect.com/science/article/abs/pii/S0003682X07001843?via%3Dihub
Michał Leszczyński
