At this stage, we are ready to do the first iteration of our Krichhoff PreSDM migration using the travel time calculation tables.
Input (what we need to provide):
1. Input to the PreSTM gathers or COMF enhanced gathers for generating the PreSDM CIG (Common Image Gathers)
2. Stack or velocity volume for mapping the trace headers
3. Travel time table
4. File name TT near (If the user chooses the option "Use near offset TT"). This is not mandatory but the rest are mandatory.
Output (what we get):
PreSDM CIGs
Visuals:
We won't get any vista items to visualize the contents of the Kirchhoff PreSDM file in/out - migration TT module
Parameters:
Minimum Offset CIG (meter) Provide the minimum offset for generating the CIG output
Maximum Offset CIG (meter) Maximum offset for generating the CIG output
Offset increment of CIG (meter) Step size of offset increment
Aperture Migration aperture
Aperture type Select either Constant or Depth variant (If the user chooses Depth variant then they should provide different apertures at different depth intervals)
3D In case of 3D, check this option
TT Net interpolation type Travel time net interpolation type. We have two options. Bilinear and Nearest
If there are two traces within a constant grid spacing and if any bin falling in between these two traces then the user can select Bilinear option to do the interpolation. The interpolation is simply a linear one.
If the user chooses Nearest then the trace which is nearest to the bin will be considered in the interpolation.
GPU interpolation type
Normalization by fold Depending on the option, normalization of the amplitudes takes place. For example if the user selects the "trace", then it will calculate the number of curves/wavefronts intersect that particular trace and accordingly it will normalize the amplitude of that particular trace. Similarly if the user chooses "sample" then for each sample how many wavefronts intersected that particular trace at that particular sample and normalizes the amplitude.
Depth samples Specify the number of depth samples. i.e. up to what depth the user wants to migrate the data with respect to depth sample ratio(meter).
Depth ratio(meter) Mention depth sample ratio.
Use near offset TT In case the user wants to image the near offsets only then they can check this option. For this, the user should provide the near offset Time travel tables in the input (File name TT near). In such cases, the user should calculate the travel times for near offsets only.
Replacement velocity Provide the replacement velocity information.
Anti-aliasing coefficient Choose between 0 and 1. Zero means no anti-aliasing
Anti aliasing step X (meter)
Anti aliasing step Y (meter)
Datum(meter) Provide the datum information. As we mentioned at the beginning of this manual, unlike the PreSTM where we migrate the data from the topography, here we need the datum information in order to do the depth imaging.
Max frequency(Hz) Provide the maximum frequency to include the imaging process
Max angle aperture(degree) Provide the maximum angle
Decimation factor This will be helpful while doing the testing to optimize the parameters and for quick turn around time.
Advanced Params
Use local storage This option is useful when the work flow executed in a cluster environment where we can assign save the output in local disk for better I/O.
Seismic file name Provide the file name in the local disk.
Advanced interpolate settings
X axis step(meter) These interpolation settings are related to TT Net interpolation. Define the step size in X&Y directions
Y axis step (meter) Interpolation step size in Y direction
Constant margin(meter)
Round Pickets True by default
Round factor 5 by default.