| 1. |
- Amundsen, Lasse, et al.
(författare)
-
Multisource encoding and decoding using the signal apparition technique
- 2018
-
Ingår i: Geophysics. - 0016-8033. ; 83:1, s. 49-59
-
Tidskriftsartikel (refereegranskat)abstract
- Signal apparition is a method for encoding sources in simultaneous multisource seismic acquisition and decoding the multisource response of the earth into its single-source responses. For M sources, encoding is performed by applying periodic sequences of period M to each of the sources along source lines. Decoding is achieved in the wavenumber domain for each frequency by solving an M × M linear system of equations. The system's matrix is the product of a Fourier matrix and an encoding matrix, the latter containing the information of the codes. The solution of the system is unique when the encoding matrix is invertible. When the encoding sequences consist of time delays applied to sources' firing times, the determinant of the encoding matrix becomes a polynomial. A unique solution to decoding then exists if the roots of the polynomial avoid the unit circle. Periodic time-shift sequences for two, three, four, and six sources are discussed. A model example of simultaneous four-source data acquisition illustrates the performance of the encoding/decoding technique for the spatially nonaliased case.
|
|
| 2. |
- Andersson, Fredrik, et al.
(författare)
-
Flawless diamond separation in simultaneous source acquisition byseismic apparition
- 2017
-
Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 209:3, s. 1793-1739
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we prove that the recently introduced method of signal apparition optimally separates signals from interfering sources recorded during simultaneous source seismic data acquisition. By utilizing a periodic sequence of source signatures along one source line, that wavefield becomes separately partially visible in the spectral domain where it can be isolated from interfering signals, processed, and subtracted from the original recordings, thereby separating the wavefields from each other. Whereas other methods for simultaneous source separation can recover data in a triangle-shaped region in the spectral domain, signal apparition allows for the exact separation of data in a diamond-shaped region that is twice as large thereby enabling superior reconstruction of separated wavefields throughout the entire data bandwidth.
|
|
| 3. |
- Robertsson, Johan O.A., et al.
(författare)
-
Source deghosting
- 2016
-
Ingår i: SEG Technical Program Expanded Abstracts 2016. - : Society of Exploration Geophysicists. ; 35, s. 71-76
-
Konferensbidrag (refereegranskat)abstract
- Marine seismic data are distorted by ghosts as waves propagating upwards reflect downwards from the sea surface. Ghosts appear both on the source-side as well as on the receiver-side. However, whereas the receiver-side ghost problem has been studied in detail and many different solutions have been proposed and implemented commercially, the source-side ghost problem has remained largely "unsolved" with few satisfactory commercial solutions available. In this paper we propose a radically new and simple method to remove sea-surface ghosts that relies on using sources at different depths but not at the same lateral positions. The new method promises to be particularly suitable for 3D applications on sparse or incomplete acquisition geometries.
|
|
| 4. |
- Robertsson, Johan O.A., et al.
(författare)
-
Source deghosting by depth apparition
- 2017
-
Ingår i: Geophysics. - 0016-8033. ; 82:6, s. 89-107
-
Tidskriftsartikel (refereegranskat)abstract
- Marine seismic data are distorted by ghosts as waves propagating upward reflect downward from the sea surface. Ghosts appear on the source side and the receiver side. However, whereas the receiver-side ghost problem has been studied in detail, and many different solutions have been proposed and implemented commercially, the source-side ghost problem has remained largely unsolved with few satisfactory solutions available. We have developed a new and simple method to remove sea-surface ghosts that is related to the recently introduced concept of signal apparition. As opposed to the temporal/ spatial source signature modulation functions used in the original signal apparition theory, our source deghosting method relies on using sources at different depths but not at the same lateral positions. The new method promises to be particularly suitable for 3D applications on sparse or incomplete acquisition geometries.
|
|
| 5. |
- van Manen, Dirk Jan, et al.
(författare)
-
Aperiodic wavefield signal apparition : De-aliased simultaneous source separation
- 2016
-
Ingår i: SEG Technical Program Expanded Abstracts 2016. - : Society of Exploration Geophysicists. ; 35, s. 102-106
-
Konferensbidrag (refereegranskat)abstract
- In wavefield signal apparition, acquisition with periodic variations in source activation parameters shifts all or part of a signal cone out to, e.g., the Nyquist wavenumber, enabling perfect separation of simultaneous-source (sim-source) data below a certain temporal frequency. Cyclic convolution in the spatial frequency domain is used to generalise the signal apparition concept to the case of aperiodic variations in the source activation parameters. The separation is formulated as a leastsquares reconstruction in the frequency-wavenumber (f k) domain. The methodology is used in combination with normal moveout correction to de-alias the sim-source separation and enables shooting on position in sim-source acquisition.
|
|
| 6. |
- Wittsten, Jens, et al.
(författare)
-
Perfect partial reconstructions for multiple simultaneous sources
- 2019
-
Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 67:3, s. 1486-1497
-
Tidskriftsartikel (refereegranskat)abstract
- A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test.
|
|
| 7. |
- Wittsten, Jens, et al.
(författare)
-
Perturbations of time shifts in signal apparition
- 2018
-
Ingår i: SIAM Journal on Applied Mathematics. - 0036-1399 .- 1095-712X. ; 78:5, s. 2840-2864
-
Tidskriftsartikel (refereegranskat)abstract
- In the field of exploration geophysics, the method known as "signal apparition" offers a different perspective on how to separate signals acquired from simultaneously fired seismic sources. The method uses a periodic sequence of small time shift variations to encode the different sources, and this choice leads to exact separation of signals in diamond-shaped regions of the frequencywavenumber domain which are twice as large compared to those recovered by other methods. In this paper we investigate the signal apparition method's sensitivity to perturbations of the periodic time shift sequence. We model (measured or unknown) perturbations in a stochastic fashion and prove that the resulting inverse problem of separating the data is still well-posed, and we demonstrate the stability by numerical simulations on a finite-difference synthetic data set generated over a complex salt model.
|
|
