Friday, June 17, 2011

0032 - Making them visible

Helmut Becker at Moreiros 2.

In the archaeoastronomy of enclosures project in course, we have been using geophysical prospection to obtain the complete (or almost complete) plans of enclosures. Helmut Becker is the responsible for that survey. He is using Caesium-magnetometry.

To do his ultra-high sensitive cs-magnetometry, he is using Geometrics cs-magnetometer G-858G in the so-called duo-sensor configuration for total field measurements. The sensitivity of the magnetometer is 20 Picotesla (0.02 nT). The spacing of the 2 sensors was set to 0.5 m – with the measuring cycle of 10 Hz (10 measurements per second) the resolution was 50 x 10 cm (50 cm distance of the profiles in the 40m-grids and 10 cm samples on the profile). This is the fastest and most sensitive method for archaeological prospecting on large areas. Almost one hectare per day could be measured with this high resolution. Measuring the geomagnetic total field rather than only the gradient of the vertical component with fluxgate-gradiometry allows a much deeper penetration into the ground (major archaeological structures can be made visible to a depth of 4 to 5 meter).

Preliminary data processing is done every night directly after the fieldwork – therefore any new ideas about the continuation of the prospecting could be immediately realized.

The results have been quite remarkable, as we can see by the examples of Xancra, Perdigões or Moreiros 2.

Next week we will be starting Monte do Olival 1 and expectations are high.

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