Surface versus borehole electrical measurements

Surface electrical measurements usually don't need any special equipment to install (other than a resistivity system). However, surface electrical measurements are limited in their ability to resolve deep features. The maximum depth electrical measurements can "see" depends on site conditions - a very loose guideline is 1/5 the array length (although this is probably optimistic in most cases).

Borehole electrical measurements generally require custom built cables, not to mention the installation of boreholes. This becomes much more labor intensive and expensive. Survey design and interpretation of results are also often more complicated than with surface measurements.

However, resolution of features between (and particularly near) the boreholes is improved and may be critical for achieving project objectives.

In either case, some pre-modeling is highly recommended to assess the likely outcomes of electrical measurements and to guide survey design.