R3t is a forward/inverse solution for 3D current flow in a triangular prism mesh. The inverse solution is based on a regularised objective function combined with weighted least squares (an ‘Occams’ type solution) as defined in Binley and Kemna (2005).

The user must define the mesh for R3t as a series of elements, each with 6 nodes. The user must also specify the position of the electrodes within the mesh. The electrodes can be located anywhere in the mesh, provided they fall on node points. Neumann (no current flow) boundary conditions are applied at the boundary of the mesh and so if a half-space is modelled then the mesh should be extended away from the region of interest to account for ‘infinite’ boundaries.

R3t will output calculated parameters (resistivity) for the entire mesh and the user must extract results for the region they wish to study. The region is parameterised in terms of resistivity blocks by grouping patches of elements.

Measurements are defined in a separate file as a set of four electrode indices. Each electrode is defined as a "borehole" number and an "electrode" number (note that the "borehole" index is used simply to help group electrode strings and does not have to refer to a "borehole"; note also that the "borehole" index can be the same for all electrodes if the user wishes not to use this labelling).

32bit and 64bit processor versions of R3t are supplied (the latter being necessary for larger problems).

References

Binley, A. and A. Kemna, 2005, Electrical Methods, In: Hydrogeophysics by Rubin and Hubbard (Eds.), 129-156, Springer.