Raw Data on Helicopter-borne Electromagnetics (HEM)

The BGR helicopter (Sikorsky S-76B) is used for airborne geophysical surveying of the Earth’s subsurface. The standard equipment comprises the methods electromagnetics, magnetics and radiometrics. The active multi-frequency, helicopter-borne electromagnetic (HEM) system consists of circular (diameter about 0.5 m) transmitter and receiver coils (horizontal separation about 8 m) housed by a flying tube (bird) about 40 m beneath the helicopter. The HEM system used before 2002 consisted of rectangular coils (horizontal separation slightly less than 7 m) and five system frequencies (0.4 - 190 kHz). The ratio of received and transmitted signal yields to the electrical conductivity down to 50/150 m depth in case of conductive/resistive subsurface.