I had a book here which documented a government study of underground
antennas. They constructed antennas underground, then used an aircraft to
take field strength measurements. The aircraft was the easiest way to do
that. However, the tests were in somewhere like South Dakota - which would
make much more sense than somewhere in the city. They probably flew patters
similar to what you describe, although I think they used a B-17 in this
study.

The conclusion of the study was that underground antennas work - but not
very well.

It very well could be some government funded research program. The problem
may be that the 182 does not burn up the money quick enough, so the study
has been going a few years.

I also recall a fellow taking regular air samples over a manufacturing
plant. He stopped when the turbine shut down because of the impurities in
the air over the smokestack.

You can get his N number and call him up and ask him (or her). But, then if
two people in suits knock on your door knock on your door, I would go out
the back.

Colin