How does VOXI treat areas within AOI that have no data?

PeterHedin

In my current dataset, acquired with a helicopter borne system, surveying went around a town that was dead-center in the area of interest to avoid the infrastructure there, and so there is a several square km large elliptical “hole” in the database. I’m using VOXI to do both magnetic and FDEM inversion, where the first is a 3D inversion and the second (if I understand correctly, and at least in the current version) is a 1D inversion followed by 3D interpolation. In both cases, the volume below this “no-data zone” at the town is populated (incl. some conductors) in the results, and I’m wondering with what?

DarrenAndrews

Hi @PeterHedin, VOXI will always fill the defined area of interest with physical property. In the magnetic case it will be inverting for the data points that are adjacent to the township; these data points will still be influenced by the physical property within the township area.

In the EM case, the 3D interpolation will interpolate through the township area from the 1D inversion of the adjacent data points, so the subsurface conductivity structure will not have the same influence on the data as in the magnetic case.

The simplest approach I would recommend in this case is to 'window' the voxels post-inversion to remove the zone of susceptibility/conductivity from the inversion area that coincides with the township.

This article describes how to create a polygon file:(https://my.geosoft.com/supportcentre#/kb/kA330000000V1hRCAS)

You can then use the polygon file to window the voxels in order to remove the zone of susceptibility/conductivity from the inversion. You can do this within our 3D viewer by going to the Voxel menu, selecting "Utilities" and then selecting "Window a Voxel". Within this tool there is an option to horizontally window the voxel using the polygon file.

Best regards,