Helicopter-borne Electromagnetics (HEM) German North Sea coast - Data

This dataset has been compiled within the BGR project "D-AERO-Auswertung" based on several survey area located along the German North Sea coast. 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, which consists of circular (diameter about 0.5 m) transmitter and receiver coils (horizontal separation about 8 m) operating at five and since 2007 at six system frequencies, is 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. The results are displayed as apparent resistivity (= half-space resistivity) and centroid depth maps at each of the six system frequencies ranging from 0.4 to 130 kHz.