2D Filtering - Seequent
Transcript of 2D Filtering - Seequent
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2D Filtering
Oasis montaj’s 2D Filtering extension offers a set of 2D filters aiming to emphasize subtle features, separate regional
residual fields, separate signals representing different depths layers, remove noise, and produce different field
components as an aid for interpretation.
Namely these filters are:
1. MAGMAP: Fourier domain filters
2. Matched Filter: Depth slice separation filter
3. Analytic signal: Resolve cross section of two dimensional potential field structures
4. Generalized derivative: Curvature response of potential field structures
5. Tilt Derivative: Rough estimate of horizontal and vertical location of magnetic sources
6. Gradient to total magnetic intensity: Magnetic field reconstruction from gradient components
Oasis montaj Fourier Domain 2D Filtering
The montaj™ MAGMAP Filtering tool provides a 2D FFT filter library to allow
the application of common Fourier domain filters to grids. MAGMAP rapidly
processes and enhances gridded datasets by applying a wide range of robust
geophysical and mathematical filters. This tool lets you easily define your own
filters, modify the filter specific parameters and apply any number of filters
together in a single operation. A Spectral filter editor provides an interactive
means of modifying the filter parameters and instantly observe the effect both
on the radially averaged power spectrum (if symmetrical) and the 2D preview
window.
The MAGMAP Filters for gridded data can be divided into 2 categories:
Potential Field Filters
• Reduction of magnetic data to the magnetic pole or equator,
• Differential reduction of magnetic data to the magnetic pole appropriate for
very large grid,
• Upward/downward continuations to a different datum,
• Apparent magnetic susceptibility calculation for magnetic field,
• Apparent density calculation for residual gravity field,
• Optimum Weiner depth filter,
• Conversion between different directional components of the magnetic field.
Use MAGMAP Filtering to:
• Process and enhance gridded datasets by
applying a wide range of two dimensional
Fast Fourier Domain filters (FFT filters),
• Apply any combination of geophysical
filters, and/or mathematical filters,
concurrently,
• Modify selected filter parameters, using
the Interactive Spectral Filter Editor, and
observe live the effect of the filter on the
radially averaged power spectrum and the
preview window,
• Define and apply custom filters,
• Customize settings to your dataset • Interpret grids using spectral analysis
products (2D and radially averaged power
spectra) models or other sources.
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General Purpose Filters
• Integer and fractional derivate in X, Y, or Z directions
• Integration in X, Y & Z
• Low/High Bandpass filters
• De-corrugation and directional filters,
• Four different potential field components calculations,
• Custom radially symmetrical filters
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Interactive Filter Editor
An Interactive Spectral Filter Builder enables users to
design and fine tune filter parameters and instantly
observe the effect of the filter(s) in the preview window,
collectively or individually.
Only the radially symmetric filters, such as low/high pass
filters will be displayed on the spectrum graph. The initial
power spectrum, the final power spectrum, the filter
coefficients of the currently selected radially symmetric
filter and the filter coefficients of the combined filter will
be displayed in real time.
The 2D output preview window is resizable and is used to
view individual or combined effect of the filters.
Matched Filter
The Matched Filter tool leverages MAGMAP to help define interactively a set of complementary filters, each filter emphasizing the signal of a defined depth slice. The matched filters are tapered bandpass filters that collectively cover the entire spectrum.
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Horizontal and vertical derivatives of potential field data are routinely
measured, and can be calculated from the observed total magnetic intensity.
The next set of tools utilize a combination of these derivatives to enhance
specific signatures in the data and are an essential part of the interpretation process.
Analytic Signal The Analytic signal of a magnetic field is a common interpretation tool that
helps resolve the cross section of two dimensional potential field
structures.
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Generalized Derivative This derivative operator is a linear combination of the horizontal and
vertical field derivatives, normalized by the analytic signal amplitude. It is
indicative of the curvature response of potential field structures.
Tilt Derivative The tilt derivatives can be used to roughly estimate the horizontal and
vertical location of magnetic bodies without taking into consideration the
nature of the magnetic source. The nature of the source can then be further investigated.
Gradient to Total Magnetic Intensity The residual magnetic field can be reconstructed from gradient
components, and used in conjunction with other data during the
interpretation process.
References
Cooper G., Cowan D.R., A generalized derivative operator for potential field data, Geophysical Prospecting, (2011) Vol
59, pp. 188-194
Hardwick, C.D., "Two Methods of Gradient-Enhanced
Gridding – A Discussion", Technical Paper., (2004)
Miller H.G. , Singh V.J., "Potential Field Tilt - a New Concept for Location of Potential Field Sources", Journal of Applied Geophysics, vol. 32 (1994), no. 2-3, pp. 213-217.
Verduzco B. et al., "New Insights into Magnetic Derivatives for Structural Mapping", The Leading Edge, vol. 23 (2004), pp. 116-119.
Salem A., Williams S., Fairhead J.D., Smith R., Ravat D., "Interpretation of magnetic data using tilt-angle derivatives", Geophysics, vol. 73 (2008), no. 1, pp. L1-L10.
Phillips J., Designing matched bandpass and azimuthal
filters for the separation of potential field anomalies by
source region and source type, ASEG extended abstract,
(2001)