Geophysics – Oval Barrow – Part 3

Following on from previous posts about the possible oval barrow near Fordingbridge (Part 1 and Part 2), I was away when two more squares were surveyed with the resistivity equipment.  I recently downloaded the data from the data logger, and produced plots of the results.  The first 20m square represented the final quadrant covering the oval cropmark, and so it was with some anticipation that I waited for the plot to draw up (click on plot to enlarge):

Oval barrow final quadrant

Oval barrow final quadrant

On seeing the plot, there was a definite band of lower readings in a diagonal arc – how would this relate to the other three squares?  The combined plot is shown below (click on plot to enlarge):

Oval barrow plot - 4 squares
The black and white visualisations in particular show how the bottom right square provided the final piece in the jigsaw, perfectly joining the other squares to complete the oval shape seen in the cropmark.  There are however some features revealed by the geophysics which were not obvious in the cropmark.  For example:

  • The ditch does not seem to form a perfect oval, with sharp turns at a couple of locations.
  • The width of the feature does not appear to be constant, being much wider to the bottom right.
  • There is a possible small central feature shown most clearly in the black and white plots.
  • There is a wide arc of low readings which seems to obscure the top left of the oval.  It may be that this is a later feature.

This extra information provided by the plot shows the benefits of approaching such investigations with a number of different survey methods.  After finishing the final quadrant, the team completed another adjacent square, shown in the combined plot below (click on plot to enlarge):

Oval plot - 5 squares

Oval plot – 5 squares

The very high readings to the extreme left may represent a change in ground conditions towards the edge of the field.  Of interest is a very thin arc of lower readings from approximately (9, 20) to (12, 7).

The field has now been sown, and so any further survey work will have to wait until next year.  However, it is clear that this particular survey has been very successful, being able to not only locate the exact position of a crop mark, but also to provide additional information about the feature.

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One Response to Geophysics – Oval Barrow – Part 3

  1. Pingback: Geophysics – large enclosure – September 2014 | The AVAS Blog

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