|
<< Click to Display Table of Contents >> Navigation: Modelling > Surface multiple modelling (2 layers) |
This module is deprecated. It is provided for legacy workflows only.
The Surface Multiple Modelling (2 layers) module generates a synthetic shot gather dataset for a two-layer subsurface model, consisting of a near-surface layer overlying a second layer. Both primary and multiple reflections from each layer boundary are modelled analytically using ray-tracing through the two-layer velocity structure. The module can generate first-order (peg-leg) and second-order (inter-bed and surface) multiples, giving control over the complexity of the multiple wavefield in the synthetic. The generated gathers are written to an output SEG-Y file and are intended for testing and validating multiple attenuation algorithms before applying them to real data.
The module has no data stream inputs; all parameters define the geometry and physical model of the synthetic directly.
This module does not require input seismic data. It generates synthetic traces from scratch based on the specified acquisition geometry and two-layer velocity model.
The spatial interval between consecutive shot positions in the synthetic geometry, in metres. This value also defines the distance unit used to compute receiver offsets. Set this to match the nominal shot interval of the real acquisition you are modelling.
Default: 25 m.
The total number of shot gathers to write to the output file. Each gather contains the same synthetic traces but with headers filled with incrementing shot coordinates. This controls the total output dataset size.
Default: 128.
The receiver spacing expressed as a multiple of the Distance between shots. The actual receiver interval in metres equals this value multiplied by the shot distance. For example, with a shot distance of 25 m and an offset increment of 4, receivers are spaced 100 m apart.
Default: 4.
The number of traces per shot gather (number of receivers per shot). Traces are evenly spaced in offset from zero to the maximum offset. Increase this to model a wider spread or more offsets.
Default: 30.
The thickness of the upper (near-surface) layer in metres. Together with the first-layer velocity, this determines the two-way travel time to the top of the second layer and the shape of the surface-multiple travel-time curve.
Default: 1000 m.
The thickness of the second (deeper) layer in metres. Together with the second-layer velocity, this determines the two-way travel time to the base of the model (the deeper reflector) and controls the timing of inter-bed multiples.
Default: 2000 m.
The propagation velocity of the upper layer, in m/s. This value is used for ray-tracing through the first layer when computing travel times for all primary and multiple arrivals. It also governs Snell's law refraction at the first layer boundary when computing diving rays for two-layer reflection travel times.
Default: 2000 m/s.
The propagation velocity of the lower layer, in m/s. This value is used for ray-tracing through the second layer to compute the travel time of the deeper primary reflection and any multiples that involve the second layer. Set the second-layer velocity higher than the first to model a realistic velocity gradient.
Default: 2500 m/s.
The output trace sample interval in seconds. This controls the temporal resolution of the synthetic traces. Use 0.002 for 2 ms or 0.004 for 4 ms sampling. The output trace length is computed automatically to include all primary and multiple arrivals.
Default: 0.004 s (4 ms).
Controls which multiples are modelled in the synthetic. Set to 0 to model primary reflections only. Set to 1 to include first-order peg-leg multiples involving both layers. Set to 2 to additionally include second-order multiples whose type is selected with the Type of 2nd order multiples parameter.
Default: 0 (no multiples).
Selects the ray path type for second-order multiple modelling when Order of surface multiples is set to 2. The code indicates how many reflections occur in each layer: 111 — a triple surface multiple that bounces three times in the first layer only; 211 — a peg-leg multiple with one deep reflection and two reflections in the first layer; 221 — two reflections in the deeper layer and one in the first; 222 — a triple multiple entirely within the two-layer model. This parameter is active only when Order of surface multiples is 2.
Default: 111.
The dominant frequency in Hz of the Ricker wavelet applied to all synthetic arrivals. Lower values produce a broader wavelet with lower temporal resolution; higher values produce a sharper wavelet. Match this to the dominant frequency of the real data you are modelling.
Default: 15 Hz.
The full path and file name of the output SEG-Y file (.sgy or .segy) where the synthetic shot gathers will be written. Use the file browser to navigate to the desired output location. The file will contain all shot gathers in sequence, with headers populated according to the defined geometry.