How to refine 3D mesh from surface (fine at top, coarse at depth) with topography?

[genfranka]

Question

Hello,

I’m running a 3D ERT timelapse inversion with fullInversion. Since this is very memory-intensive, I can’t just make the mesh as fine as I would like everywhere.

What I really need is a mesh that is fine at the surface (where the electrodes and most structures of interest are) and gets progressively coarser with depth.

I’ve tried a few things already:

-Creating a synthetic cube with stacked regions: works in principle, but then I lose the real electrode positions and topography that I need for inversion.

-Exporting to Gmsh and applying refinement: also not really successful so far.

-Adding RegionMarkers to the 3D PLC and Refining based on that (that would maybe be the easiest option but somehow it doesnt work)

-Manually adding Refinment Nodes to the PLC based on their distance to the surface (works, but the quality of the mesh gets really bad and I feel like this is not the way)

So my question is: Is there a way to create a 3D mesh that is refined near the surface and coarser at depth, while still keeping real topography and electrode positions correct for inversion?

Has anyone faced a similar issue and found a working solution?

Thanks a lot!