Method to maintain towed dipole source orientation

Apparatus and method for a steerable horizontal electric dipole source system for underwater deployment as a moving source in electromagnetic surveying of subsurface regions for hydrocarbons. Position locating sensors (195) are placed near each electrode (26, 27), and means (197, 198) are provided for correcting the electrodes to be at the same elevation with azimuth aligned with the source tow line (11) and the electrode mid-point positioned over the source tow line, based on instantaneous location information from the sensors. The streamer (28) connecting the electrodes may also be monitored for shape by sensors, with corrections made by lateral and vertical control means disclosed herein. The invention can be applied to any marine streamer used in geophysical surveys, including a towed streamer (191) of electromagnetic or seismic receivers (192).