Not entirely sure that this is a "Surveying" topic (mods do we need another Technical forum for science/technology?) but here goes ...

Previously someone asked about ground penetrating radar, which got me thinking about the possibility of using cave radio systems for "prospecting". One of the opportunities that cavers have over "normal" geophysics is that we are already in the ground and so can send signals from within a cave to both other underground locations and to the surface.

Given that water filled passage and soil filled passage are likely to have different conductivity than the surrounding rock would they transmit radio more easily? Could mud filled tunnels be made to act as leaky feeders so that the route could be traced on the ground above? Has anyone tried any of this in a caving context?

For that matter has anyone tried using other geophysical techniques (seismic, resistivity etc.) cave-to-surface and/or cave-to-cave?