ground penetrating radar

I was delighted to find that there actually was
already a preliminary experiment on ground penetrating
radio on the Moon.

Apollo-17 conducted a SEP experiment, which is
described in some detail at this link.

http://www.hq.nasa.gov/office/pao/History/alsj/a17/a17.summary.html

The ALSEP station contained a radio transmitter. The
lunar rover carried an antenna, and it measured
variations in
the strength of the signal cuased by changes in
electrical conducitiy of the subsurface soil.

Cool.

A proof of concept at least.