Which Geoelectric Array Sees the Deepest in Noisy Environment? Depth of Detectability Values of Multielectrode Systems over Various Two- Dimensional Models

In urban environment, the two dominating difficulties of any geophysical measurements are as
follows: (1) the area available for measurements is restricted, therefore the length of geoelectric layout
is also limited; (2) the noise level is high, and the noise diminishes the maximum depth, where any
subsurface target can be detected from. We determined depth of detectability values (i.e. the
maximum depth values at which still useful information is obtained about a given inhomogeneity at a
given noise level) from results of two-dimensional numerical model computations assuming
multielectrode (electrical resistivity tomography) measurements. We carried out depth of detectability
studies for six various geoelectric arrays, assuming various noise levels. As it has been found, the
depth of detectability is both array-and model dependent. Therefore in a field study it is advisable to
select an array, which has the greatest possible depth of detectability values for the given model at
the given noise level. When there is no a priori assumption about the subsurface model, as a default
selection we recommend either the pole-dipole (P-DP) array or the dipole axial (DP-ax) array, since
for the most models we studied they dispose with the largest depth of detectability values. A twofold
increase in the noise level may lead to a decrease of approximately two in the depth of detectability
itself.