zaterdag 26 maart 2011

The antenna guy

Ben walking with the magnetometer
Johannes helping Ben with the GPR
Archaeology is not about digging anywhere. There are more and more ways to discover if there are archaeological features beneath our feet before excavation. And that is exactly the job of Benjamin, our Antenna Guy. His antenna is actually a magnetometer, an instrument that measures spatial variations in the strength of the magnetic field. The presence of iron, brick, burned soil and certain rocks causes anomalies in the Earth´s magnetic field and the magnetometer reacts strongly to these. The information is transformed into a grey-scale map that allows archaeologists to locate possible features. Unfortunately, it is not always easy to distinguish man-made features from natural phenomena. Besides, subtle features maybe hidden by highly magnetic materials.
Ben spends his days walking with his antenna or with his ground penetrating radar (GPR) between small red and white flags, recording the strength and velocity of the soil´s magnetic response. During this process, no one is allowed in the area: a belt buckle or even a paper clip would interfere and would be registered as anomalies by the magnetometer.
After one week of work, the results come out: the hill´s magnetic map is relatively homogenous, except for an area north of trench C, which shows a strong magnetic anomaly. The excavation does not yield any solid archaeological structure though. We nevertheless notice that the soil of the area contains numerous small metallic balls (about 1mm in diameter). Are they natural? Are they residues from metal working? Opinions are divided. We hope that the analysis of the samples will give us an answer.