Wednesday, 12 June 2013

Noise Attenuation: Which filter(s) to use?

GeoTeric's data conditioning suite now encompasses both targeted noise attenuation and spectral enhancement. Within the noise cancellation suite there are a series of different filters that allow the user to tailor each noise removal to the data and objectives. The examples below illustrate the effect of different filters on a series of faulted channels, offshore NW Australia.

The SO FMH (Structurally Orientated: Finite Median Hybrid) filter is a noise reducing, edge-preserving filter. It removes coherent noise, such as, minor acquisition or migration noise whilst preserving subtle details like edges, corners and sharp dips in the structure. Minor acquisition or migration noise Structurally Oriented Noise filtering retains much more detail than traditional smoothing techniques, as it uses dip and azi volumes to steer the smoothing filter.

TDiffusion is a noise reducing, adaptive edge preserving filter targeting random noise. The idea is to repeatedly process a volume with a low pass filter to produce a series of increasingly smoother, images by solving a Partial Differential Equation through time. The filter is anisotropic since it adapts to local orientation and adapts the direction of the filter. The TDiffusion filter differs from the SO filters described previously in that the orientation information embedded in the structural tensor enables the TD

SO Noise filter is a Structurally Orientated operation and targets aggressive noise such as salt or basalt effects. It is not as sophisticated as the SO FMH or TDiffusion filter and may not maintain edges. It retains much more detail than traditional smoothing techniques as it does not smooth across the geology. The Structurally Oriented noise filters can be applied along an orientation defined by the local structural vector at each point in the data.

Many data sets require attenuation of both coherent and random noise; in these instances it is imperative to run the SO FMH filter before the TDiffusion filter. The TDiffusion filter will ‘see’ any coherent event as signal, thus preserving noise within the data. If the coherent noise is attenuated with the SO FMH filter the TDiffusion filter will attenuate the remaining random noise.

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