In a resistivity survey, how do we calculate the depth of penetration for a Schlumberger array?
$\begingroup$ I thought I had this in a book (GSL Field Geophysics pocket book), but alas not. Of course the electrical field is continuous so you are going to have a depth that represents something like "half the sensitivity is shallower than this". $\endgroup$– winwaedSep 17, 2014 at 13:06
Short answer: 0.2 times the total length of your cable(s).
100m rollout --> ~20m depth
Bear in mind that the deeper you get, the more you have to be careful with your data interpretation. Also if you do a roll-along your depth doesn't get deeper.
Long answer see Bernard J (2003): Short note on the depth of investigation of electrical methods. Heritage Geophysics.