I have some noisy neighbours and I've thought of the same idea for controlling noise in neighbourhoods. You could have a microphone on every lamp post and send people fines for violating the rules.
It's over the EPA regulations, it's neighborhood wide, and it is on for 2 hours between 11pm and 1am on random days. The EPA did monitoring of the house and site but couldn't pinpoint where it was coming from because of how low frequency it was.
This isn't surveillance, this is the equivalent of finding who is dumping raw sewage in your drinking water.
For 20Hz noise, are there too many reflections to use an oscilloscope with 3 mics on a 25ft baseline to triangulate it (you'd have to elevate the mics)?