HGG has a GCM system (DUALEM421S), which can be operated on land or water. The GCM system operates at a frequency of 9000 Hz, and has 2 receiver coils in a distance of 1, 2 and 4 meter from the transmitter, respectively. The instrument makes a unique measurement 10 times per second and can be operated by boat, walking or towed behind a motorized vehicle. A GPS, which is connected to the system, ensures detailed positioning of the measurements. The logging of positioning and GCM data is controlled by in-house developed software which ensures data synchronization and easy in-field data evaluation. Mapping lines can be plotted and visualized, to make sure that the desired line spacing and areal coverage is obtained.