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Datuming is the process of deriving wavefields at one datum
from those at another datum. There is great utility in this process
for land static correction (Berryhill, 1979, 1984;
Shtivelman and Canning, 1988; Bevc, 1992)
and for layer replacement in migration
(Berryhill, 1979, 1984; Yilmaz, 1987).
There are two ways to do it. One is by simple
time shifting along individual traces, as in first-stage
land data static correction.
The other is by wavefield extrapolation based on the wave equation.
Datuming is closely linked to migration; both need to extrapolate
the wavefields from one datum to another.
Several methods of wavefield extrapolation have been developed for migration,
among them, finite-difference methods
(Claerbout, 1976, 1985), Kirchhoff-integral methods (French, 1975;
Schneider, 1978), f-k methods (Gazdag, 1978; Stolt, 1978), and
reverse-time migration methods (Baysal et. al., 1983; McMechan, 1983).
For datuming, Berryhill (1979, 1984) applied
the Kirchhoff-integral method to
wavefield extrapolation. But his method is only easy to implement
and accurate in a constant velocity medium.
When the velocity of the medium varies, his method
encounters various problems associated with the approximate
solution to the wave equation and further difficulty in doing the ray tracing.
Shtivelman and Canning (1988) presented an extrapolation scheme based on the
asymptotics of the Kirchhoff-integral solution to the 2-D scalar wave equation.
Their method is similar to that of Berryhill (1979), though more accurate.
Bevc (1992b) implemented the datuming scheme given
by Berryhill (1979) with the addition
of being an anti-aliasing approximation to the Kirchhoff-integral.
The inclusion of
anti-aliasing of the Kirchhoff-integral has a low-cut filtering effect on
the resulting wavefields.
Ji et al. (1992) applied phase-shift method to perform datuming
(Gazdag, 1978; Reshef, 1991);
this method has the difficulty of implementing lateral velocity variations.
Popovici (1992) applied phase-shift plus interpolation
(PSPI) to perform datuming; but implementation of PSPI is clumsy in an
irregular geometry.
This paper proposes a method of datuming that uses the exact two-way acoustic
wave equation to do
wavefield extrapolation along with depth migration. This method is
implemented in the space-time domain by the finite-difference method.
The paper first demonstrates upward and downward datuming for poststack data.
It then demonstrates upward and downward datuming for
prestack common-shot gather and common-receiver gather data
and suggests application procedures for seismic data static correction
for irregular land topography.
Tests with synthetic data show good results.
This method of datuming shows great promise for applications
in land data static correction
and migration in complex velocity areas.

** Next:** POSTSTACK DATUMING
** Up:** Mo: Datuming
** Previous:** Mo: Datuming
Stanford Exploration Project

11/17/1997