Table 2.

Results of qualitative assessment of ERT 2D profiles (both least-squares and robust inversions) based on the accuracy of the cleared wall foundation position and on the cleared wall foundation being successfully imaged

2D profile number (see Fig. 2) and array typeLeast-squares inverted model, r.m.s. % error misfitCleared wall foundation well definedRobust inverted model, r.m.s. % error misfitCleared wall foundation well defined
NS1, Wenner5.0Good2.8Moderate
NS1, dipole–dipole5.0Good2.7Moderate
NS1, pole–dipole4.1Poor2.8Poor
NS1, pole–pole9.3Poor5.5Poor
NS2, Wenner4.4Moderate2.2Poor
NS2, dipole–dipole5.0Moderate3.4Poor
NS2, pole–dipole8.8Poor4.1Poor
NS2, pole–pole9.2Poor4.4Poor
NS3, Wenner9.4n.a. (off axis)4.8n.a. (off axis)
NS3, dipole–dipole10.3n.a. (off axis)5.2n.a. (off axis)
NS3, pole–dipole5.3n.a. (off axis)3.4n.a. (off axis)
NS3, pole–pole14.9*n.a. (off axis)7.1n.a. (off axis)
EW1, Wenner5.0Good3.1Moderate
EW1, dipole–dipole6.4Good4.6Moderate
EW1, pole–dipole6.8Moderate4.4Poor
EW1, pole–pole12.7*Poor7.6*Poor
EW2, Wenner3.4Good2.0Moderate
EW2, dipole–dipole10.1Good5.0Moderate
EW2, pole–dipole3.4Moderate2.0Moderate
EW2, pole–pole12.0*Poor5.7Poor
EW3, Wenner1.8n.a. (off axis)2.5n.a. (off axis)
EW3, dipole–dipole2.8n.a. (off axis)1.7n.a. (off axis)
EW3, pole–dipole2.4n.a. (off axis)1.5n.a. (off axis)
EW3, pole–pole13.9*n.a. (off axis)6.3n.a. (off axis)

Images were ranked ‘Good’ when the model achieved both parameters, ‘Moderate’ when the model achieved only one and ‘Poor’ when the model did not achieve any parameters. Model r.m.s. inversion percentages are also included. n.a., not applicable.

  • * Indicated relatively high model errors.