This section provides an overview of the data quality control measures and inversions completed on the Mt. Isa data sets. The DC data is first discussed. The conductivity from those inversions are then used for IP inversions.

DCR Data

The ultimate goal is to generate a 3D subsurface conductivity model. However, we first carry out 2D inversions. The three main reasons for this are:

  1. Data were collected in a 2D geometry, that is, the transmitter and receiver electrodes are along one line.

  2. The geology is principally 2D so the inversion results will provide an approximate result and/or maybe a starting model for a subsequent 3D inversion.

  3. 2D inversions are quick to perform and can reveal possible issues with data (e.g., bad data points, incorrect normalizations, etc.)

Data Quality Control

As presented in the previous section, the MIMDAS system collects simultaneously a pole-dipole (P-DP) and a dipole-pole (DP-P) data configuration. Accordingly, the P-DP and DP-P data were inverted separately in 2D. The uncertainties are assigned as 5% of the data amplitude with a minimum floor value of 0.02 mV. The data were inverted and no noticeably bad data points were obvious in the data misfit maps. This also means that data were correctly normalized so they corresponded to a unit amplitude current in the transmitter. The figure below shows the observed and predicted data and recovered models for both configurations and for each of the ten 2D lines. There are some regions where there are significant differences in the conductivities obtained from the P-DP and DP-P configurations. Some of this might be attributable to the fact that the two surveys illuminate buried conductors quite differently due to current channeling. Overall, however the inversion results have the same general distribution of conductivity and there doesn not appear to be major issues with normalizations or bad electrodes.

Table 14 : Independent 2D inversions of the P-DP and DP-P DCR data

Once Loop Reflect