Question

Nine equally spaced electrodes are placed along a profile to perform Dipole–Dipole multi-electrode resistivity imaging. The maximum number of data points that can be obtained at measurement level \(n=2\) is:

• A. 5
• B. 6
• C. 4
• D. 2

Hint:

In a multi-electrode dipole–dipole survey, the number of usable data at a given level is obtained by sliding the two dipoles (length \(a\)) along the line with center separation \(n a\), stopping one spacing before the line ends to limit end effects.

Answer 1

The Correct Option is A

Step 1: Definition for \(n=2\).
For a dipole–dipole array, each dipole (AB and MN) has length \(a\). At measurement level \(n=2\), the centers of the current and potential dipoles are separated by \(2a\). Step 2: Enumerate valid configurations with 9 electrodes.
Label electrodes \(1,2,\dots,9\). Using \(n=2\), the valid pairs (current dipole \(AB\) ; potential dipole \(MN\)) that fit on the line while keeping at least one spacing from the profile ends (to avoid end‐effects) are: \[ (1,2;\,3,4),\ (2,3;\,4,5),\ (3,4;\,5,6),\ (4,5;\,6,7),\ (5,6;\,7,8). \] That gives \(\boxed{5}\) data points at level \(n=2\).