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The module forward modelling /
tomography allows the calculation of the complete
electromagnetic or seismic wavefield for a 2-dimensional subsurface
model. In addition a 2- and 3-dimensional tomographic approach
based on SIRT (simultaneous iterative reconstruction technique)
is integrated for the inversion of transmission traveltime data. The
module is useful for the following applications:
GPR (Ground penetrating radar)
reflection seismics
refraction seismics
borehole/borehole transmission
Forward modelling
The module forward modelling allows the calculation of the
complete electromagnetic or seismic wavefield for a 2-dimensional
subsurface model. You may interactively edit any layer boundary and some
predefined elements (e.g. circle or rectangle). The physical parameters
may vary along the boundary whereby lateral changes are easily defined.
The parameters are entered within a table which also may be used for
entering the boundary values (see right figure above). The forward
modelling is done using a Finite Difference scheme solving the
Maxwell equations (elastic wave equation, respectively). 3 different
sources are implemented: point- source, plane wave and exploding
reflector model. Using the point source you may model the wave
propagation from any point in the model (e.g. a transmitter at the
surface). The exploding reflector model allows the modelling of a
complete zero offset section in only one step. The complete wavefield or
a single line is stored. The complete wavefield may be interpreted
within the 3D-datainterpretation, the single line may be processed and
interpreted like any 2D-data line.
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Tomography
A 2- and 3-dimensional tomographic approach based on SIRT
(simultaneous iterative reconstruction technique) may be used for the
inversion of transmission traveltime data. The geometries of the
individual sources and receivers are arbitrary.
The figure at the lower left corner shows a synthetic example. The
starting model is interactively constructed and may contain any kind of
inhomogeneities. The geometry of the rays may be loaded into the
starting model (see right figure below). The ray- tracing contained in
the SIRT-algorithm is restricted to straight rays. An extension to
curved rays based on a network raytracing solution is in preparation.
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