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LNA by local Radon (Linear Noise Attenuation) suppresses coherent linear and near-linear noise — such as ground roll, guided waves, and air-wave noise — from pre-stack seismic gathers using a local parabolic Radon transform. Unlike conventional Radon-based demultiple methods that operate over the full gather, this module applies the Radon transform within a sliding local window defined by a user-drawn velocity line on the gather display. Events that fall within the defined slowness (p-value) pass zone are preserved; all other coherent energy — including the targeted noise — is attenuated.
The optional LNO (Local NMO) correction pre-flattens each event to the reference velocity before applying the Radon filter, improving the separation quality when the signal and noise have similar apparent velocities at near offsets. After filtering, the LNO correction is reversed. Input gathers must be sorted by CMP-offset. The module inherits the standard sequence infrastructure and supports a difference-mode display to show the removed noise.
The primary data connection carrying the seismic dataset. Transports the SEG-Y file handle, trace headers, and geometry objects through to the output.
The pre-stack seismic gather to be filtered. Must be CMP-offset sorted. The gather is displayed in the interactive panel where velocity lines are drawn to define the noise zone to be attenuated.
Half-width of the local sliding window in traces used to compute the Radon transform around each target event. Default: -1 (all traces). When set to -1, the full gather is used as a single window (equivalent to a global Radon transform). Setting a positive value (e.g., 15–30 traces) confines the transform to a local neighbourhood, which can better separate noise that is spatially localised.
Minimum curvature (slowness) modelled by the Radon transform, in seconds. Default: -0.5 s. Defines the lower bound of the parabola range. For ground-roll attenuation this should be sufficiently negative to encompass the residual moveout of the ground roll at far offsets.
Maximum curvature modelled, in seconds. Default: 1 s. Defines the upper bound of the parabola range. Computation time increases with the square of the number of p-values.
Curvature sampling interval at the reference offset, in seconds. Default: 0.008 s. Smaller values improve resolution but increase computation time.
Controls whether the P and Tau taper windows reject (zero out) or preserve the energy within the defined zone. Default: enabled (reject). When enabled, the energy inside the taper window (the noise zone defined by the P tapers) is attenuated and the energy outside is preserved. Use the P tapers group to define the slowness range of the noise to be rejected.
Reference source-receiver offset at which the parabolic curvature is defined, in meters. Default: 500 m. The p-values (P min, P max, P tapers) are all defined at this offset. Set this close to the maximum offset of the gather for best results.
Container group defining the trapezoidal taper window in the slowness (p) dimension of the Radon domain. The taper is defined by four values: P 1 (ramp-on start, default -0.2 s), P 2 (ramp-on end, default -0.1 s), P 3 (ramp-off start, default 0.1 s), P 4 (ramp-off end, default 0.2 s). When Reject tapers is enabled, energy with p-values between P 1 and P 4 is attenuated (with linear transition zones at the ramp edges). Set these to encompass the slowness range of the noise you want to remove while protecting reflections near p = 0.
Container group defining a time (tau) taper applied to the Radon spectrum. Defaults: Tau 1 = 0 s, Tau 2 = 0.05 s, Tau 3 = 10 s, Tau 4 = 10.05 s. By default the taper covers the entire record — adjust these if you want to restrict noise attenuation to a specific time zone only.
Lower frequency limit of the Radon filter pass-band, in Hz. Default: 0 Hz. Set to the lower edge of the usable signal band.
Upper frequency limit of the Radon filter pass-band, in Hz. Default: 100 Hz. Set to the upper edge of the usable signal band.
Stabilisation factor for the least-squares Radon inversion, as a percentage of maximum spectral power. Default: 0.5 %. Increase this if the output contains numerical instabilities.
When enabled, applies automatic gain control equalisation to the gather before the Radon transform and removes it afterwards. Default: enabled. AGC balances amplitudes so that weak deep reflections receive equal weight to strong shallow events during the transform.
Length of the AGC operator window, in seconds. Default: 0.5 s. Only used when Use AGC is enabled.
When enabled, applies a Local NMO (LNO) correction before the Radon transform to pre-flatten reflections to the reference velocity. The correction is reversed after filtering. Default: enabled. Enable this when signal and noise have similar apparent velocities and the standard p-domain separation is insufficient. The LNO parameters (T0, Reference velocity, Coefficient) control the pre-flattening correction.
Zero-offset intercept time for the LNO correction, in seconds. Default: 0 s. Together with Reference velocity, this defines the hyperbolic moveout curve used for LNO pre-correction. Only used when Use LNO is enabled.
Reference NMO velocity used for the LNO pre-correction, in m/s. Default: 2000 m/s. Set this to the approximate velocity of the primary reflections in the target zone. Only used when Use LNO is enabled.
Fractional strength of the LNO correction applied, from 0 (no correction) to 1 (full correction). Default: 1. Reduce this value to apply only a partial pre-correction when the reference velocity is uncertain. Only used when Use LNO is enabled.
When enabled, the module automatically connects to adjacent modules in the processing flow.
Number of CPU threads used for parallel processing. Set to the number of available physical cores for best performance.
When enabled, this module is bypassed and the input data passes through unchanged.
The output data connection carrying the noise-attenuated dataset.
The gather with linear noise attenuated, preserving the reflection events outside the defined p-taper zone. The difference between the input and output (showing only the removed noise) can be inspected in the module's difference display panel.