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Computes Amplitude Versus Angle (AVA) attributes from NMO-corrected pre-stack gathers using the Shuey approximation (2-term or 3-term). For each time sample, the module performs SVD least-squares regression on the amplitude vs. angle curve to decompose the reflection response into geophysically meaningful components: Intercept (I, the zero-angle reflectivity), Gradient (G, the rate of amplitude change with angle), and optionally the C term (3-term Shuey only). The results are output as separate gather volumes for further AVO/AVA interpretation or crossplotting.
The Shuey approximation is valid for angles up to approximately 30–35 degrees. Use this module after NMO correction and offset-to-angle conversion, before AVO attribute extraction or inversion workflows. A minimum of 3 valid traces per gather is required for regression. Ensure the angle gather type (degrees or radians) matches the Input angles type parameter setting to avoid silent result corruption.
NMO-corrected pre-stack seismic gathers. The data must be fully NMO-corrected and muted before input. Residual NMO will corrupt the amplitude-vs-angle relationship and degrade attribute quality.
Angle gather computed by the Vrms to Angle module, containing the incidence angle for each trace. Must be co-registered with the NMO gather (same CDP sorting). The unit (degrees or radians) must match the Input angles type parameter setting.
Two-way travel time (ms) used only for the interactive crossplot visualization display — shows the amplitude-vs-angle regression at this specific time sample. Does not affect the output volumes. Default: 0.
Maximum incidence angle (degrees) to include in the AVA regression. Traces with angles exceeding this limit are excluded. The default value of 90 degrees includes all traces — in practice, set this to 30–40 degrees since the Shuey approximation becomes unreliable at larger angles. Using angles beyond 35° will introduce non-linear effects that corrupt the Intercept and Gradient estimates.
Selects the Shuey approximation order. 2Term (default) computes Intercept and Gradient only, suitable for most AVO workflows up to ~30°. 3Term additionally solves for the C curvature term, requiring wider angle coverage (typically >30°) and more traces per gather for a stable regression solution.