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<< Click to Display Table of Contents >> Navigation: Velocity > Create Velocity Corridor |
Note: This module is deprecated and is retained for compatibility with legacy processing flows. It is recommended to use current velocity analysis and corridor generation tools for new projects.
The Create Velocity Corridor module automatically constructs a velocity picking corridor from a semblance (correlation) stack and an initial interval or RMS velocity field. The corridor is a band centered on the interpolated velocity, used to constrain manual or automatic velocity picking to a geophysically plausible range.
The module operates in three stages. First, it detects reflector positions in the correlation (semblance) stack by finding the peak semblance value within overlapping windows controlled by the Trace aperture and Sample aperture parameters. Second, it reads the initial velocity at each detected reflector position and spatially interpolates these sparse velocity picks into a continuous velocity field using fast Kriging interpolation. Third, it writes the resulting velocity corridor to a polygon file (.corr) that defines, at every output grid node, the lower bound, central velocity, and upper bound of the permitted picking corridor. The interpolated velocity gather is also produced as a visual output.
Use this module when you want to guide velocity picking within a known velocity range derived from a pre-existing velocity model and a semblance panel, ensuring that picks stay within a geologically consistent corridor.
The initial velocity gather, typically a time-velocity (Vrms) or interval velocity field displayed as a gather in the time-velocity domain. This data provides the velocity values that are sampled at reflector positions detected in the semblance stack and then interpolated to fill the full output grid. The quality and accuracy of the corridor depends directly on this input: ensure that the velocity field is geologically reasonable and covers the full time range of interest before running the module.
The semblance or correlation panel corresponding to the same data as the Initial Time Velocity. This gather contains semblance energy values in the time-velocity domain. The module scans this panel to find local semblance maxima — that is, positions where the stack energy is highest — which correspond to the dominant reflectors and their moveout velocities. Higher-quality semblance panels (good signal-to-noise ratio, clear velocity discriminability) result in more accurate reflector detection and a more reliable corridor.
The number of traces that form each search window in the spatial (trace) direction when scanning the semblance panel for reflector peaks. The semblance panel is divided into non-overlapping windows of this width, and only one peak point is extracted per window. Default value: 10 traces. Minimum value: 1. Smaller values extract more reflector picks along the spatial axis, providing denser Kriging control points but potentially including noise peaks. Larger values produce fewer, more stable picks but may miss lateral velocity variations. Use smaller values only if the semblance panel has high signal-to-noise ratio and you need to resolve rapid lateral velocity changes.
The number of time samples that form each search window in the time direction when scanning the semblance panel for reflector peaks. One peak is extracted per window in this dimension as well. Default value: 20 samples. Minimum value: 1. Together with Trace aperture, this parameter controls the density of the reflector control-point grid passed to the Kriging interpolator. A larger value extracts fewer picks along the time axis, which is appropriate when reflectors are sparsely distributed in time. A smaller value captures more time detail but increases sensitivity to semblance noise between reflectors.
The number of nearest control points used by the Kriging interpolator when estimating the velocity at each output grid node. Default value: 50 points. Minimum value: 1. A larger aperture means each interpolated value is influenced by more distant picks, resulting in a smoother velocity field. A smaller aperture makes the interpolation more local, better capturing abrupt velocity changes but potentially creating discontinuities where pick density is low. For most surveys a value between 30 and 100 provides a good balance between smoothness and local fidelity.
A representative average velocity of the medium, used as a scaling factor to convert the time-axis sample index into a physical distance (depth proxy) when computing spatial coordinates for the Kriging interpolation. Specify this value in m/s. Default value: 3000 m/s. Minimum value: 1500 m/s. Set this to a value representative of the overall velocity of the section being analyzed. For shallow surveys dominated by sediments, a value around 1800–2200 m/s may be more appropriate. For deep crystalline basement sections, values above 4000 m/s may be needed. An incorrect value here distorts the geometric distances used by the Kriging interpolator and can produce a poorly shaped corridor.
The half-width of the velocity corridor, in m/s. At every output grid node, the corridor is defined as: lower bound = interpolated velocity − corridor width; upper bound = interpolated velocity + corridor width. Default value: 25 m/s. Minimum value: 1 m/s. A narrow corridor (small value) tightly constrains velocity picks to stay close to the interpolated model velocity, which is useful when the initial velocity model is known to be accurate. A wider corridor allows more flexibility in picking, accommodating uncertainty in the model or datasets with complex velocity heterogeneity. Typical values range from 25 m/s (tight constraint) to several hundred m/s (loose constraint) depending on geological complexity and model confidence.
The full path and filename for the output velocity corridor polygon file. The file is written in .corr format, which is a tab-delimited text file. Each record in the file contains the spatial coordinates (X, Y), the two-way time of the grid node, and the lower bound, central, and upper bound velocities of the corridor at that location, together with angular bounds. This file can subsequently be loaded into a velocity picking session to constrain picks within the computed corridor. You must specify this path before running the module; the module will report an error if no output file is set.
The Kriging-interpolated velocity field, delivered as a velocity gather in the time-velocity domain. This gather has the same spatial and temporal dimensions as the Initial Time Velocity input, but its values have been replaced by the spatially interpolated velocity estimated from the reflector picks extracted from the semblance panel. This output can be displayed as a velocity overlay to visually verify that the interpolated corridor is geologically consistent before applying it to velocity picking. It does not replace the input velocity model; it is the smooth approximation used to center the corridor.