Thursday, July 24
(Previous entries available here)

Hello, from Norma and Adrian Challands on this warm, sunny day in Orkney.

We count ourselves lucky to be working on Brodgar and are currently carrying out tomography surveys.

Adrian has worked in Orkney practically every year – sometimes 3 or 4 times a year – since 1987, when he did geophysics at Barnhouse, and I have helped and dug on many Orkney sites too.

We live in North Cambridgeshire, near Peterborough, where we met both Jane and Colin at Etton, of the famed causewayed enclosure. Bob Randall, who developed the TRS equipment we use for both resistivity and tomography, lives in the next village.

Whereas resistivity surveys take readings on a square grid in plan, tomography surveys take resistance readings in section – like, for instance, a bran scan which also employs tomography.

We are placing 40 probes, spaced at 0.5m intervals and equal depths, and taking readings on each probe, increasing the spacing at each of seven or eight runs.

The software produces readings in the shape of an inverted, truncated pyramid – representing a depth of 2m or so from the ground surface.

What we are looking for are stone holes between the standing stones and stubs.

No luck so far, but we have only done one survey. Now we are off to do more.