Schematic illustration of the Porpoise surface-towed CSEM system. The system includes a 40 m horizontal electric dipole (HED) source that emits a current of 100 amps, and 4 Porpoise receivers at increment distance ~250 m to form a 1 km array. Each Porpoise includes a 2 m inline electric dipole, a data logger, and a GPS unit. At the end of the array, a Dorsal towed unit consists of an altimeter, conductivity/temperature measuring device and a GPS unit.