Magnetometry
- Created by: ktommo
- Created on: 03-05-17 20:34
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- Magnetometry
- Magnetic distortions caused by past human activity.
- Topsoil contains haematite which has some magnetic forms.
- A ditch filled with topsoil will contain more haematite than the surrounding area.
- It's fill will therefore be slightly different magnetically and this difference may be detected by sensitive modern magnetometers.
- Another distortion is where topsoil has been exposed to considerable heat.
- This erases the magnetic properties of the iron oxide.
- When the soil cools, the iron oxides become permanently magnetised according to the polarity of the earth's magnetic field at the time.
- Since this field changes over time, the site of kilns and hearths appear as magnetic anomalies.
- Can be used to rapidly scan quite large areas of soil, grass and crops to highlight anomalies.
- Used in detailed site investigations where they can detect small features up to 1m down.
- To be able to detect anomalies, the magnetic background of the soil has to be measured and magnetometers calibrated against it.
- Sensitive magnetic instruments are easily disturbed by iron, including nails, pipes and wire fences as well as the zips and piercings worn by archaeologists.
- Another limitation can be background interference from magnetic bedrock or where a long period of occupation has left a magnetic layer over a wide area.
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