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RMO by picking is an interactive module for detecting and correcting Residual Moveout (RMO) on pre-stack CMP gathers using a semblance-based velocity scan. The module computes a semblance panel around the existing RMS velocity model within a user-defined velocity search window, and allows the user to pick or auto-pick the residual velocity correction on each gather. The picked corrections are used to update the RMS velocity model, producing a corrected velocity field for re-application of NMO or subsequent processing steps. This is a standard step in iterative velocity refinement workflows between NMO correction and stacking.
Container for the standard input data connections. Connect this to the output of the preceding module in the processing sequence.
The input seismic CMP gather on which the RMO semblance is computed and the residual velocity correction is picked. This gather is typically NMO-corrected before being passed to this module.
An optional super-gather formed by stacking or averaging traces from several neighbouring CMPs. Using a super-gather improves the signal-to-noise ratio of the semblance panel, especially on sparse or noisy datasets. Connect this to a super-gather output from the velocity analysis workflow, or leave disconnected to use only the single CMP gather.
The input RMS velocity model used as the reference around which the residual velocity scan is performed. The semblance is computed over a range of ±Velocity window around this model. Connect this to the output of a velocity analysis or velocity model builder module.
The interactive picking connection that links this module to the location map, allowing the user to select the CMP position at which to perform velocity picking. This connection is used for interactive gather-by-gather navigation during the picking session.
When enabled (default: true), the module automatically picks the peak semblance at each time sample using the auto-picker parameters. When disabled, the user picks the residual velocity correction manually on the semblance panel display. Use automatic mode for a first-pass solution on large 3D surveys; switch to manual mode for QC and fine-tuning of the picks.
The half-width of the velocity search range (in m/s) centred on the reference RMS velocity model. The default is 500 m/s. The semblance panel spans ±Velocity window around the input velocity at each time sample. Increase this value if large residual moveout is expected; decrease it for fine residual corrections near a good velocity model.
The velocity increment (in m/s) between adjacent trial velocities in the semblance scan. The default is 50 m/s. A smaller step increases the resolution of the semblance panel but increases computation time. The number of trial velocity panels is equal to 2 × Velocity window / Step velocity.
The time window (in seconds) used to smooth the semblance panel before picking. The default is 0.05 s (50 ms). Smoothing suppresses noise spikes in the semblance and produces more stable picks. Use a longer window on noisy data; use a shorter window to preserve high temporal resolution in the velocity correction.
Container group for parameters controlling the stretch mute applied during the RMO correction.
The maximum allowable NMO stretch as a fraction (default: 1 = 100%). Samples that would be stretched beyond this factor relative to zero-offset are muted. Decrease this value to apply a more aggressive stretch mute, suppressing large-offset NMO artefacts.
The length (in samples) of the smoothing operator applied to the velocity correction curve in the time direction. The default is 10 samples. Higher values produce a smoother, more gradually varying velocity correction; lower values follow the semblance picks more closely.
The absolute minimum velocity (in m/s) allowed in the output corrected velocity model. The default is 1000 m/s. Picks or model values below this floor are clipped to this value. Set this to a physically reasonable lower bound for the survey area to prevent unrealistic velocity corrections.
The absolute maximum velocity (in m/s) allowed in the output corrected velocity model. The default is 6000 m/s. Picks or model values above this ceiling are clipped to this value.
The time window (in seconds) used to normalize the semblance energy before display and picking. The default is 0.1 s (100 ms). This normalization corrects for varying trace energy with depth and improves the visibility of semblance peaks at different two-way times.
Selects the semblance weighting method. The default is None (standard semblance). Weighted applies amplitude-based weighting to enhance high-amplitude coherent events. Similarity-weighted uses a cross-correlation similarity measure that is less sensitive to amplitude variations.
The exponent applied to the amplitude weighting in the weighted semblance computation. The default is 0 (no weighting). Positive values increase the relative weight of high-amplitude events; negative values reduce their influence. Only relevant when Weighted semblance is set to Weighted.
Container group for auto-picker parameters. These parameters are only active when Auto picker mode is enabled.
The minimum semblance value (as a fraction from 0 to 1, default: 0.1) required for a sample to be considered a valid auto-pick. Time samples with semblance below this threshold are not picked, and the velocity at those times is interpolated from neighbouring picks. Increase this value to restrict auto-picks to high-confidence semblance maxima.
The minimum time separation (in seconds) between adjacent auto-picks. The default is 4 s. Only one semblance maximum is allowed within this time window, which prevents the auto-picker from generating multiple closely spaced picks in the same semblance event. Reduce this value to allow finer temporal picking resolution.
The velocity-axis border width (in m/s) near the edges of the semblance panel that is excluded from auto-picking. The default is 0 m/s. Set a non-zero value to prevent the auto-picker from picking at the extremes of the velocity search range where edge effects may create false semblance maxima.
The time-axis border (in seconds) near the top and bottom of the gather that is excluded from auto-picking. The default is 0 s. Set a non-zero value to skip the shallow and deep sections of the gather where the semblance is unreliable due to noise or limited offset coverage.
The near-surface velocity (in m/s) used in the RMO correction when surface topography is accounted for. The default is 1800 m/s. This value is used to convert the elevation datum correction to a time shift at each offset, analogous to the V0 parameter in multifocusing and mute-factor calculations. Set this to the velocity of the weathering layer or replacement velocity used during statics corrections.