IPC Definitions - January 01, 2012
E21B 47/125 - Definition
This group covers:
Processes or apparatus in which the transmission link is through the ground.
Attention is drawn to the following places, which may be of interest for search:
Magnetic or electric prospecting | G01V 3/00 |
Electronic transmission systems in which the earth is the medium | H04B 13/02 |