Estimation of wavelet and source radiation pattern by reverse time extrapolation

1989 ◽  
Author(s):  
Philip M. Carrion ◽  
Selma dos S. Sacramento ◽  
Reynam da C. Pestana
Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1026-1035 ◽  
Author(s):  
Philip M. Carrion ◽  
Selma dos S. Sacramento ◽  
Reynam da C. Pestana

In a typical seismic experiment (land or marine), the generated source wavelet is either unknown, or known only approximately. In order to solve many geophysical problems, an accurate wavelet estimation is crucial. This paper demonstrates a fast numerical algorithm which allows not only estimating the source wavelet but also its angular spectrum (radiation pattern) from plane‐wave decomposed seismograms. Surprisingly, literature on this subject is virtually missing, although a nonuniform angular spectrum of the generated wavelet can substantially affect the recorded data. The technique presented here is based on the downward continuation (DC) and reverse‐time extrapolation (RTE) of the recorded data (both pressure and its vertical derivative). The proposed method is iterative: The rate of convergence does not depend on phase characteristics of the generated wavelet. We demonstrate that both the wavelet signature and its angular spectrum can be estimated accurately from plane‐wave seismograms. We also illustrate the technique on a variety of wavelets with different amplitude/phase characteristics.


Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1514-1524 ◽  
Author(s):  
Edip Baysal ◽  
Dan D. Kosloff ◽  
John W. C. Sherwood

Migration of stacked or zero‐offset sections is based on deriving the wave amplitude in space from wave field observations at the surface. Conventionally this calculation has been carried out through a depth extrapolation. We examine the alternative of carrying out the migration through a reverse time extrapolation. This approach may offer improvements over existing migration methods, especially in cases of steeply dipping structures with strong velocity contrasts. This migration method is tested using appropriate synthetic data sets.


Geophysics ◽  
1994 ◽  
Vol 59 (4) ◽  
pp. 597-609 ◽  
Author(s):  
Wen‐Fong Chang ◽  
George A. McMechan

By combining and extending previous algorithms for 2-D prestack elastic migration and 3-D prestack acoustic migration, a full 3-D elastic prestack depth migration algorithm is developed. Reverse‐time extrapolation of the recorded data is by 3-D elastic finite differences; computation of the image time for each point in the 3-D volume is by 3-D acoustic finite differences. The algorithm operates on three‐component, vector‐wavefield common‐source data and produces three‐component vector reflectivity distributions. Converted P‐to‐S reflections are automatically imaged with the primary P‐wave reflections. There are no dip restrictions as the full wave equation is used. The algorithm is illustrated by application to synthetic data from three models; a flat reflector, a dipping truncated wedge overlying a flat reflector, and the classical French double dome and fault model.


Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. H27-H33 ◽  
Author(s):  
Jun Ji

To reduce the migration artifacts arising from incomplete data or inaccurate operators instead of migrating data with the adjoint of the forward-modeling operator, a least-squares migration often is considered. Least-squares migration requires a forward-modeling operator and its adjoint. In a derivation of the mathematically correct adjoint operator to a given forward-time-extrapolation modeling operator, the exact adjoint of the derived operator is obtained by formulating an explicit matrix equation for the forward operation and transposing it. The programs that implement the exact adjoint operator pair are verified by the dot-product test. The derived exact adjoint operator turns out to differ from the conventional reverse-time-migration (RTM) operator, an implementation of wavefield extrapolation backward in time. Examples with synthetic data show that migration using the exact adjoint operator gives similar results for a conventional RTM operator and that least-squares RTM is quite successful in reducing most migration artifacts. The least-squares solution using the exact adjoint pair produces a model that fits the data better than one using a conventional RTM operator pair.


Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. T103-T122 ◽  
Author(s):  
Yulang Wu ◽  
George A. McMechan

A challenging outstanding problem in reverse time extrapolation is recovering accurate amplitudes at reflectors from the receiver wavefield. Various migrations have been developed to produce accurate image locations rather than correct amplitude information because of inadequate compensation of attenuation, dispersion, and transmission losses. We have evaluated the requirements, and determined the theoretical feasibility, of true amplitude recovery of 2D acoustic and elastic seismic data by using the analytic Zoeppritz equations for plane-wave reflection and transmission coefficients. Then, we used synthetic acoustic and elastic wavefield data generated by elastodynamic finite differences to verify the recovery, in the reverse time propagation, of spherical waves and illustrated the salient differences between the incident wavefields reconstructed from reflection data only and from the combination of reflection and transmission data. These examples quantitatively verify that recovering an incident plane or a spherical wave requires the reverse time propagation of all reflections and transmissions in a model with the correct velocity and density. Accurate reconstruction of an incident wave is not possible by backward propagation of only reflections. As an application, we removed downgoing internal multiple reflections generated by upgoing waves incident at reflectors shallower than a horizontal well, in which geophones are deployed. The subtraction of the downgoing reflection involves wavefield reconstruction at depths shallower than the horizontal well and separation of upgoing and downgoing wavefields. This approach assumes that the correct acoustic (or elastic) velocity and density models are available in, and shallower than, the layer where the horizontal well is located. Incident-wave reconstruction works equally well for smooth models, as for models with sharp boundaries. Uncertainties in the model used for reconstruction, and incompleteness of the data aperture are propagated into the equivalent uncertainties, and incompleteness of the reconstruction.


Geophysics ◽  
1991 ◽  
Vol 56 (3) ◽  
pp. 390-396 ◽  
Author(s):  
G. A. McMechan ◽  
R. Sun

Much of the energy removed in a typical standard seismic data preprocessing sequence corresponds to approximately horizontal propagation in very near‐surface structure. Such energy includes direct (first‐break) compressional waves, direct shear waves, and ground roll; these may be effectively separated from deeper reflections by downward continuation of the recorded common‐source wavefield, by reverse‐time extrapolation, to a depth beneath which these waves propagate. The subhorizontally traveling waves get left behind in the shallow part of the model. Subsequent upward continuation of the wavefield reconstructs the original surface‐recorded wavefield with the subhorizontally traveling waves removed. Only a very simple (even constant) velocity distribution is required for the wavefield extrapolation; no net distortion is produced since both downward and upward continuations are performed using the same velocity model.


1988 ◽  
Vol 32 (1) ◽  
pp. 62-69 ◽  
Author(s):  
Jaromír Janský ◽  
Jan Zedník ◽  
L. Ruprechtová

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