Patent ID: 7805249

Claim:
A method for performing a controlled source electromagnetic survey of a subterranean region using two or more electromagnetic transmitters such that the combined responses at a receiver can be separated according to the electromagnetic transmitter, comprising: (a) selecting or constructing N mutually orthogonal waveforms, one for each of the N electromagnetic transmitters, where N=2 or more. wherein waveform mutual orthogonality is based on one of the following or a combination of both: (i) waveforms are chosen that have no common frequencies with non-negligible associated amplitudes in their frequency spectra, using a predetermined criterion for negligible; (ii) waveforms are constructed from repetition of a selected waveform element with one or more predetermined phase shifts applied to the selected element, said phase shifts being chosen such that when combined data are binned on a selected time interval then transformed bin-by bin to the frequency domain, data from each of the electromagnetic transmitters can be separated by virtue of the phase shifts, said selected bin time interval being a selected integer multiple of the waveform element's duration wherein said selected integer is two or greater; (b) energizing each of the electromagnetic transmitters to repetitively transmit its waveform, all of the electromagnetic transmitters transmitting at the same time; (c) recording a combined electromagnetic response to the multiple concurrent transmissions at one or more receivers; and (d) delivering the recorded combined response data for processing to separate the data by binning the data on a predetermined time interval and then transforming the data, bin-by bin, to the frequency domain, the bin time interval being determined by said waveforms' periodicities.