Electromagnetic surveying using a crossed electric dipole transmitter with selectable orientations

摘要

Various controlled source electromagnetic survey methods for surveying subterranean strata are described. The methods rely on an electromagnetic source 22 comprising two orthogonal horizontal electric dipole transmitters Tx, Ty. Broadcast signals from the two transmitters combine to provide a corresponding resultant virtual dipole transmitter v. The effective orientation of the resultant dipole transmitter v may be arbitrarily selected so that data for arbitrary transmitter orientations may be provided (e.g. inline or broadside as desired). This is achieved without needing to move a source around, or to provide separate sources for each desired orientation. In some examples, a desired resultant virtual transmitter orientation may be provided by applying appropriately scaled drive signals Sx, Sy to the two transmitters. In other cases, a desired effective resultant virtual transmitter orientation may be provided by applying equal drive signals to the two transmitters, but scaling the receiver signals associated with each transmitter relative instead. I.e. in some cases the relative scaling may be applied at the transmission stage, and in other cases the relative scaling may be applied at the detection stage.