De-aliased source separation method
Methods are described for separating the unknown contributions of two or more sources from a commonly acquired aliased wave field signals including the determination of models with reduced support in the frequency-wavenumber domain which reconstruct the wave fields of independently-activated sources after a coordinate-transform of the acquired wave field data and/or in a coordinate-transformed domain.
1. A method, comprising:
obtaining wave field recordings based on activation of at least two sources along one or more activation lines, including varying at least one parameter between the sources from one activation to another, the at least one parameter being one or more of a source signal amplitude, a source signal spectrum, a source activation time, a source location at activation time, and a source depth, such that the varying causes one or more scaled replications of a wave field with limited, cone-shaped support in the frequency-wavenumber domain of at least one of the at least two sources along a wavenumber axis or axes with the one or more scaled replications partially overlapping a wave field with limited, cone-shaped support of one or more of the other of the at least two sources, with the wave field with limited cone-shaped support of the one or more of the other of the at least two sources being either not affected or replicated and scaled by the varying;
separating, by processing circuitry, a contribution of at least one of the at least two sources to the obtained wave field recordings as generated by the at least two sources individually, in the absence of the other of the at least two sources;
reducing, by the processing circuitry, an aliasing ambiguity in a result of the separating step, which is caused by the one or more replications partially overlapping, by applying at least one coordinate transformation to the obtained wave field recordings;
generating, by the processing circuitry, a sub-surface representation of structures or Earth media properties from the contribution of at least one of the at least two sources; and
outputting the generated sub-surface representation.
2. The method of claim 1 , wherein the coordinate transformation, when represented in the wavenumber-frequency domain, reduces the support of the scaled and replicated cone-shaped supports of the at least two sources, or an amount of energy corresponding to each source in regions of overlapping support.
3. The method of claim 1 , wherein the at least one coordinate transformation imposes a bandwidth limitation in certain directions by means of directionality penalties.
4. The method of claim 1 , wherein the separating step further comprises:
modelling the obtained wave field recordings using a model that incorporates the varying in the at least one parameter to relate representations of wave fields generated by the at least two sources individually in a transform domain to the model of the obtained wave field recordings,
using the model, inverting the obtained wave field recordings to separate a contribution of at least one of the at least two sources to the obtained wave field recordings.
5. The method of claim 4 , where the separating step includes incorporating an effect of the at least one coordinate transformation by relating coordinate-transformed representations of the wave fields to the coordinate-transformed wave field recordings.
6. The method of claim 3 , wherein the at least one coordinate transformation includes computing signal energy directions of one or more of the at least two sources in the space-time domain using separated source contributions from non-overlapping parts of the obtained coordinate-transformed wave field recordings.
7. The method of claim 1 , wherein the at least two sources are activated simultaneously or near-simultaneously.
8. The method of claim 1 , wherein the at least one coordinate transformation is inverted to obtain a full non-coordinate-transformed signal.
9. The method of claim 1 , wherein the at least one coordinate transformation is one of an NMO correction, a parabolic transform, and a local coordinate transformation representing a local directionality structure.
10. The method of claim 5 , where the separating step further comprises computing an exact expression for an NMO stretch or a filter that models an effect of NMO on a modulation function associated with the varying of the at least one parameter.
11. The method of claim 1 , wherein the separating step is performed in a time-varying manner after time-frequency decomposition of the coordinate-transformed wave field recordings.
12. The method of claim 9 , further comprising applying simultaneously multiple NMO corrections by solving linear systems.
13. The method of claim 12 where the linear systems are solved iteratively.
14. The method of claim 1 , wherein the separating step is performed in one of a Fourier transform domain, a Radon transform domain, a Gabor time-frequency domain, and a tau-p transform domain.
15. The method of claim 14 , wherein operations in a domain of separation are replaced by respective representations or mathematical equivalents in corresponding transformed domains in the space or time domain.
16. The method of claim 1 , wherein at least one of the at least two sources is a virtual source, and the method is applied for at least one of source-side deghosting and receiver-side deghosting.
17. The method of claim 1 , further comprising at least one of estimating a redatuming operator on a source side and estimating a redatuming operator on a receiver side.
18. The method of claim 1 , wherein the obtained wave field recordings include multiple components, and one or more of the multiple components is separated, and has an aliasing ambiguity reduced, using information derived from one or more of the other multiple components.
19. The method of claim 1 , wherein the at least one parameter is varied in a non-periodic manner.
20. The method of claim 1 , wherein the at least one parameter is varied in a non-periodic manner and is composed of a periodic part overlaid non-periodic fluctuations.
21. An apparatus, comprising:
processing circuitry configured to
obtain wave field recordings based on activation of at least two sources along one or more activation lines, including varying at least one parameter between the sources from one activation to another, the at least one parameter being one or more of a source signal amplitude, a source signal spectrum, a source activation time, a source location at activation time, and a source depth, such that the varying causes one or more scaled replications of a wave field with limited, cone-shaped support in the frequency-wavenumber domain of at least one of the at least two sources along a wavenumber axis or axes with the one or more scaled replications partially overlapping a wave field with limited, cone-shaped support of one or more of the other of the at least two sources, with the wave field with limited cone-shaped support of the one or more of the other of the at least two sources being either not affected or replicated and scaled by the varying;
separate a contribution of at least one of the at least two sources to the obtained wave field recordings as generated by the at least two sources individually, in the absence of the other of the at least two sources;
reduce an aliasing ambiguity in a result of the separating step, which is caused by the one or more replications partially overlapping, by applying at least one coordinate transformation to the obtained wave field recordings;
generate a sub-surface representation of structures or Earth media properties from the contribution of at least one of the at least two sources; and
output the generated sub-surface representation.