Studies on Multiplication of the Depth of Detectability Using γ11n Arrays

Depth of investigation (DI) is a basic parameter of all geophysical methods, including geoelectrics.
The depth from which one can get information has always been a crucial parameter in the
geophysical exploration. This paper deals with the depth of detectability (DD) of 2D electric resistivity
tomography configurations. DD is the maximal depth from which a given model body is detectable in
the presence of a given noise level. Based on previous DD calculations for conventional electrode
arrays it is shown in this paper that there is a nearly linear relation between the maximum value of
their parameter-sensitivity (PS) maps and their DD values. Studying the PS maps of other arrays, as
well, we found that many of them have higher PSmax values than those of the conventional arrays.
These so-called γ11n arrays are therefore expected to have larger DD values, too. The performed DDcalculations
have confirmed this expectation. γ11n arrays are linear geoelectric arrays where γ refers
to the CPCP order of the current (C) and potential (P) electrodes while the subscript numbers refer to
the distance of the neighbouring electrodes. In case of the studied prism and dyke models the γ11n
arrays – if n is larger or equal to 2 - consistently produced higher DD-values than the best
conventional arrays. The DD value of these arrays can be even 2-3 times larger than that of the best
conventional array value. Such an increase in the DD value is especially useful if the available place
for measurements is limited, e.g. due to infrastructural conditions. Anomalies in large depth, for
example, which are not seen by traditionally used arrays, may become detectable using γ11n arrays
as it was verified also by numerical studies. These arrays require moreover less measurement than
most conventional arrays resulting in shorter measuring time. According to the above observations the
γ11n arrays and particularly the γ11n, γ11n- and γ11n ones can be useful alternative of the conventional
arrays particularly in sites where the place available for measurements is limited (e.g. built up areas),
because they able to give information from larger depth. Measurements with these arrays are
moreover less time consuming.