Geosoft mapping software for geophysics, geology, geochemistry
 

montaj MAGMAP Filtering

The montaj™ MAGMAP Filtering extension provides a 2D-FFT filter library to allow the application of common Fourier domain filters to gridded data in Oasis montaj.

MAGMAP rapidly processes and enhances gridded datasets by applying a wide range of robust geophysical and mathematical filters. The extension lets you define your own filters, modify the filter specific parameters and apply any number of filters together in a single operation.

Interactive Spectrum Filter

Allows you to quickly preview filtered grids. The MAGMAP Interactive Spectrum Filter solution is a dynamic visual tool that provides an interactive slider allowing you to adjust filter parameters and preview the results instantly.

SEG-Y Reader
MAGMAP Interactive spectrum filter Click to view full image

Now it's easy to experiment. You can quickly preview how each filter enhances specific features you are considering before applying the filter to your entire grid.

Use montaj MAGMAP to:

  • Apply two dimensional Fast Fourier Domain filters (FFT Filters) to gridded data
  • Potential Field Filters
  • Reduction of magnetic data to the magnetic pole or equator
  • First/second/nth vertical derivatives, including fractional derivatives
  • Upward/downward continuations to any horizontal surface
  • Apparent magnetic susceptibility maps from magnetic field
  • Apparent density maps from residual gravity field
  • Optimum Weiner depth filter
  • Conversion between different directional components of the field
  • Apply General Purpose Filters
  • Six different regional/residual separation filters
  • De-corrugation and directional filters
  • First/second/nth horizontal derivatives

New in release 7.2

Additional Gridfill option: Multi-step Expansion algorithm
MAGMAP Multi-step Expansion gridding option Click to view full image

Additional Gridfill option: Multi-step Expansion algorithm

We have added a Multistep Expansion (MSE) algorithm option to our Gridfill routine.

It is useful in minimizing artifacts when working with grids that have jagged edges and short wavelength features.

The MSE filled area also has a more natural look and is truer to the power spectra of the original data.

Find out more: How the muti-step algorithm works

The MAGMAP process requires the gridded data to be periodic and free of dummies. Traditionally MAGMAP offered two extrapolation methods to ensure this requirement; Inverse Distance Weighting (IDW)and Maximum Entropy Prediction (MEP), the latter being the default method. After filtering, the data is masked back to its original coverage, IDW skirts the grid with values rapidly decreasing to the background. MEP calculates a series of coefficients based on adjacent real segments, then uses these coefficients to recursively extrapolate the data. MEP performs well for most grids of geophysical nature by extrapolating the gridded data on a row by row basis.

This is done independently for each cardinal direction. For this very reason, in the odd case, where the edge of the grid is very jagged, and is laced with short wavelength features, the power spectrum may suffer of high frequency bias/contamination, resulting in edge effects. The artefact may spill some distance into the grid.

To address this artefact in Oasis montaj 7.2 the Multistep Expansion (MSE) algorithm has been introduced. Using MSE the filled area has a more natural look and is truer to the power spectra of the original data, while still conforming to all the FFT requirements. MSE first adds a smooth buffer ribbon around the edge of the grid, then fills all dummy islands and inlets by mirror imaging the adjacent real data, mimicking periodicity it proceeds to fill the smallest bounding rectangle of the real data calling upon the minimum curvature algorithm, and finally extrapolates the grid to the extended FFT dimension using the Linear Prediction algorithm. This method takes longer that the MEP method, thus the MEP remains the default method.

 

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