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The V depth to angle module converts a depth-domain NMO-corrected prestack gather into an angle gather. For each trace in the input gather, the module uses the local interval velocity model and a ray-parameter approach to determine the reflection angle corresponding to every depth sample and its source-receiver half-offset. The result is a gather whose values represent the angle of incidence (in radians) at each depth level, ready for AVO analysis or angle-dependent amplitude extraction.
The angle conversion relies on ray-parameter integration through the interval velocity field. A near-surface reference velocity (V0) defines the starting slowness of the ray, and the module integrates downward through the velocity column to compute the lateral offset accumulated for each ray angle and depth. The computed angle at each depth-offset pair is then linearly interpolated and, optionally, smoothed along the depth axis. Use this module in depth-domain AVO workflows after NMO correction and depth conversion have been applied.
The depth-domain prestack gather that has already been NMO-corrected. All traces must share the same datum elevation — the module validates this and will report an error if source and receiver datums differ across traces. The depth axis is used to align the angle calculation with the velocity model, so the gather sample interval and datum must be consistent with the velocity gather supplied below.
The interval velocity field stored as a depth-domain gather, where each trace holds the velocity as a function of depth at a given surface location. The module selects the velocity trace nearest to the bin location of the input data gather using a spatial search. This velocity profile drives the ray-parameter integration that converts offsets to angles. The datum of this velocity gather must match the datum of the input NMO gather.
The near-surface reference velocity (m/s) used as the starting velocity for the ray-parameter calculation. The ray parameter for each candidate angle is computed as p = sin(angle) / V0, which then governs how rapidly the ray bends as it travels through the subsurface velocity gradient. Set this value to the average P-wave velocity in the uppermost part of the section, typically the near-surface or water-layer velocity. The default value is 1800 m/s. Using a value that is too low can produce physically unrealistic ray angles and should be avoided; using a value that is too high will underestimate the computed angles.
The half-length of a running-average smoothing window (m) applied to the computed angle values along the depth axis for each trace. After the initial angle conversion, each depth sample is replaced by the average of all samples within this window centred on that sample. Smoothing reduces rapid fluctuations in the angle field that can arise from thin-layer velocity contrasts or interpolation artefacts, producing a cleaner angle gather for AVO analysis. The default value is 50 m. Set this parameter to 0 to disable smoothing entirely. Larger values produce smoother angle gathers at the cost of vertical resolution; use values comparable to the dominant wavelength in the depth domain as a practical starting point. The valid range is 0 to 10000 m.
A depth-domain gather in which each sample value represents the reflection angle of incidence (in radians) for the corresponding trace offset and depth. Traces retain the same geometry as the input NMO gather. Samples for which a valid angle could not be computed (for example, because the ray becomes evanescent for that offset-depth combination) are filled with a default value of pi/2. The output gather can be used directly for angle-dependent amplitude extraction, AVO attribute computation, or as input to angle-stack workflows.