Multi Mod

Multiple Body Inverse Magnetic Modelling

Magnetic modelling becomes very challenging when multiple bodies are involved.  The magnetic anomalies interfere with each other and one is faced with the task of decomposing the complex profile to isolate the components due to each body.  This is at best very difficult and usually not possible at all (particularly at low latitudes).  Scott Hogg & Associates has developed a versatile inverse magnetic modelling program that allows the user to simultaneously model up to five bodies.  The program works directly with Geosoft® format grids and databases.

To start the process, the profile data and grid are loaded into the program.  With a few mouse clicks, the user is able to define the bodies to be modeled, as well as select profile segments.  The background grid is not limited to total field mag.  A user may elect to display an enhanced gridded product such as vertical derivative to aid in the body definition process.  Individual model scenarios can now be created as combinations of a profile segment with one to five bodies.

The image to the right shows a number of digitized bodies, with a sample model scenario.  The selected bodies in the chosen model scenario are colour coded to correspond with the modelling screen. 

The example is taken from Ontario Airborne Geophysical Survey 1211, Attawapiskat Area

 

The images to the left and below are from the modelling screen (annotations have been added).  In the fitting process, bodies may be selectively turned on or off and the various parameters may be locked at a fixed value or allowed to float during the inversion.

The response of each model body is shown graphically, along with the sum total model response and the measured magnetic profile.   A weighting function allows one to concentrate the fit on a subset of the full profile.  Bodies may be introduced one at a time, until the entire profile response is fit.

In this example, the left hand side of the profile (south end of the segment) is only considered initially and bodies C, D and E are switched off.  Ultimately, the other bodies are 'switched on' and the entire problem is solved.  The body paramaters may be exported in a table, represented graphically on a map, or summarized in a single comprehensive report (shown below).