A NUMBER of modern techniques were used at Gleaston Castle this week as part of the non-intrusive archaeological geophysical surveys. While preserving the nature of the site, these methods can give those involved a good idea of the site's mysteries.


Magnetometry

The technique of measuring and mapping patterns of magnetism in the soil and what lies beneath it. Within a marked out grid, readings on a magnetometer detect magnetic properties in different materials (eg soil, stone, ditches, pits).

The result is that those using magnetometry can then create a map of what materials and objects lie under the surface without the need for digging.


Resistivity

This is when an electrical current is passed through the ground at regular intervals in a marked out survey grid. The tool, known as a resistivity meter (pictured above), is a frame usually with two or four metal points called electrodes.

These points are inserted into the ground and a weak electrical current passed between them. The resistivity beneath the surface to these electrical currents is recorded. Such things as copper or water offer low resistance, whereas stone, pottery or air offer high resistance.

This gives those involved the ability to map out things under the surface such as walls or ditches that may be invisible at ground level.


Ground-penetrating radar 

GPR is a take on a conventional radar and involves sending radio signals into the soil beneath. The signals are reflected back by different variations under the ground.

It is very effective at detecting structures and has become a valuable tool in detecting buried parts of buildings such as tombs, crypts or cellars, as well as showing up building foundations.