Stationary source for marine electromagnetic surveying

A method of electromagnetic surveying comprises actuating one or more electromagnetic sources being stationary in a body of water and detecting electromagnetic field signals with sensors towed through the body of water, and might be implemented over an environmental zone with restrictions on source discharges. A system to implement this method comprises a sensor streamer 14 with a plurality of electromagnetic sensors 30 disposed at spaced apart positions and a source assembly 4 at a stationary position. The system may further comprise a survey vessel 12 for towing the streamer and a vessel 6 (e.g. a ship, a boat or a floating container) for carrying the source assembly, which might comprise two or three pairs of electrodes 8 on two or three source cables 10 secured on the vessel, the pairs of electrodes defining sources with mutually orthogonal axes, i.e. between 80 and 100 degrees. The electrodes constituting one of the electromagnetic sources may be places at different depths in the body of water while the electrodes of another source are placed near the bottom or on the seabed 20.