Resistivity is a well proven method for making bulk measurements of the Earth's electrical properties. It has been used by geophysicists for many years, and can work in soil conditions where radar cannot penetrate. IRC can design and conduct such surveys as required. It is a convenient method for estimating radar losses in advance of the more expensive radar survey work. The method requires that electrodes be placed in the ground in one of several standard patterns, as shown in the figure below. The induced voltage is measured with two of the electrodes and used to compute the resistivity (or conductivity) of the soil. as the electrodes are moved further apart , the current and hence the measurement moves deeper into the ground.

One can make a low resolution two-dimensional model of a line across a site by constructing a 'pseudo-section' similar to the one shown below. The software to do this is well known and can be downloaded from the Web, at

http://www.giscogeo.com/pages/resabsw.html

A discussion on geophysical methods for cavity detection can also be found at;

http://www.geophysics.co.uk/mets2.html#2dr