Direct measurements of the ELECTRIC field in any surface conditions - blocky rock masses, run of hill, ice, snow, pavement, road surface... The ERA's technology of resistivity method exposes the best sensitive to subsurfce resistivity variations as well as a simplicity in theory and in field operations.
Wide range of resistivity methods and principles - from traditional DC and electrode arrays to sophisticated "active" electrodes, directed antennas, linear transmitter and reciever trails, automated resistivity imaging