|
<< Click to Display Table of Contents >> Navigation: Velocity > Extraction Velocities to Picking |
Note: This module is deprecated. Use current velocity analysis and picking workflows for new projects.
Extraction Velocities to Picking converts a VRMS (root-mean-square velocity) gather into a structured velocity picking corridor item. For each selected trace, the module samples the velocity field at regular time and trace intervals, and assembles a set of pick points — each defined by a velocity value, a two-sided velocity corridor width, and an angle-based corridor width — into a picking corridor collection. The resulting picking item can be used as a velocity corridor constraint in downstream migration or multi-focusing workflows.
When an optional correlation (semblance) gather is connected, the module refines the pick location within each time window to the semblance peak rather than using a fixed sample grid. This improves pick accuracy in zones of high velocity contrast. Without the correlation gather, picks are placed on a regular sample grid defined by the Sample step parameter.
After execution, the velocity picking corridor is displayed interactively in the velocity panel. The interval velocity derived from the picks via the Dix equation is also shown as a QC overlay. Picks can be saved to a corridor file (.corr) using the Save picking action.
Connect the VRMS velocity gather produced by a velocity analysis module. This gather must be in the time domain and contain one trace per CMP location, where each sample value represents the RMS velocity at that two-way time. This is the primary input from which pick points are extracted. The gather dimensions (sample interval, number of samples) define the output picking grid.
Optionally connect a semblance or correlation gather that has the same geometry as the velocity gather. When connected, the module uses the semblance values to refine the position of each pick within its time window: instead of selecting the sample at the nominal step boundary, the module searches the neighbouring samples around each step position and snaps the pick to the highest semblance peak. This produces picks that align with genuine reflector velocities rather than arbitrary grid points. If this input is not connected, all picks are placed at regular Sample step intervals.
This item is the output velocity picking corridor. After execution it holds the full set of per-trace velocity corridors extracted from the VRMS gather. Connect this to downstream modules that require a velocity corridor constraint, such as migration parameter setup or multi-focusing engine inputs. The picking can also be saved to a .corr file using the Save picking action.
Controls how frequently pick points are extracted along the time axis of each trace. A value of 1 (default) places a pick at every sample. Increasing this value — for example to 5 or 10 — reduces the number of picks per trace, which results in a coarser but smoother picking corridor. Use larger values when the velocity field is expected to vary slowly with time; use the default value of 1 when detailed time resolution is required or when no correlation gather is connected (uniform sampling mode). When a correlation gather is connected, the module still searches within the window defined by this step to find the local semblance maximum. Units: samples. Default: 1.
Controls how frequently pick curves are extracted along the spatial (trace) axis of the velocity gather. A value of 10 (default) means that one picking corridor is created for every 10th trace. Reducing this value creates a denser lateral set of corridors and gives better spatial resolution of the velocity field, but increases computation time and the size of the resulting picking item. Increase this value when the velocity field is laterally smooth or when processing large datasets where a coarser lateral sampling is acceptable. Units: traces. Default: 10.
Defines the angular half-width of the velocity corridor around each pick point in the velocity-time domain. This angle is converted internally from degrees to radians and stored as the dip component of each pick. A wider angle results in a broader corridor at later times (where the velocity-time relationship has larger curvature), naturally accounting for velocity uncertainty that increases with depth. For a tight velocity constraint, use a small angle such as 10–20 degrees. For a permissive corridor that allows more velocity variation, use a larger value such as 40–60 degrees. Units: degrees. Default: 40.
A time-varying table that defines the absolute velocity corridor half-width (in m/s) as a function of two-way time. Each row in the table consists of a time value (in seconds) and a corresponding velocity corridor width (in m/s). Between table entries the module linearly interpolates the corridor width; above the first entry the first width is used; below the last entry the last width is used. This allows the corridor to widen at greater depths, reflecting the natural increase in velocity uncertainty with depth.
At least one row must be present; the module will report an error and stop if the table is empty. A typical entry might be Time = 0 s and Velocity Corridor Width = 300 m/s, meaning that all picks are surrounded by a ±300 m/s window. Add multiple rows to define a depth-dependent corridor — for example 200 m/s at 0 s, 400 m/s at 2 s, and 600 m/s at 4 s. Sub-parameters: Time (seconds, default 0) — the two-way time at which the corridor width applies; Velocity Corridor Width (m/s, default 300) — the half-width of the velocity corridor in velocity units at that time.
Saves the current velocity picking corridor to a file in the g-Platform corridor format (.corr). A file-save dialog opens for you to choose the output file name and location. The saved file contains the full set of per-trace velocity corridors, including the central pick curve, the velocity corridor widths from the Time Velocity Width Corridor Table, and the Angle Corridor Width. The .corr file can be loaded back into other modules as a velocity corridor constraint. This action is only available after the module has been executed and a valid picking item has been created.