Annual Report 2000 - WIT

100
weight during the stacking process, dynamic wavefield attributes need to be known,
which in turn enables us also to sort the migrated/demigrated output by angle instead
of offset, thus yielding AVA curves.
0 0.5 1 1.5 2 2.5 3
Time (sec)
¢
Time Domain
Distance (km)
2 3 4 5 6 7 8 9 10
£
Section
Kirchhoff Migration
Shot/Receiver Location
x
Macro Model Information
Distance [km]
3.5 4 4.5 5 5.5 6 6.5 7 7.5
¡
z
Kirchhoff Demigration
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Depth [km]
Migrated image
Depth Domain
Figure 1: Principle of time/depth transformations by using Migration/Demigration
based on the Unified Approach.
THE UNIFIED APPROACH
We give an brief outline of the concept of the unified approach which is the underlying
theory to the method presented in this paper. A more complete discussion of the theory
and implementation can be found in Hertweck et al. (this issue). As shown by (Tygel
et al., 1996), there exists another inverse to the Kirchhoff migration integral that has
the same integral structure. It is given by a stacking process which is applied to the
depth migrated section. The stacking surfaces are now the isochrones, i.e., the surface
of equal reflection time for a given source and receiver pair. These isochrones are
defined by the same traveltimes as Kirchhoff-type diffraction traveltime surfaces that
define the stacking surface for migration. Thus, the same macro-velocity model as
previously used for Kirchhoff migration can be taken to transform the data. We can
then set up an integral transformation pair to convert from time to depth and vice