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Magnetometry Guide

Magnetometry is one of the most common geophysical techniques used in archaeology. This guide covers how to get the best results from your magnetic data using DIG.

Understanding Magnetic Data

Magnetometers measure small variations in the Earth's magnetic field caused by buried features. Fired clay (like hearths or kilns), brick walls, and filled-in ditches all have distinct magnetic signatures.

  1. Clip Data: Often, very strong signals from modern metal (like horseshoes or nails) can wash out the subtle signals from archaeology. Clipping the data to a range of -10 to +10 nT is usually a good starting point.
  2. Zero Mean Traverse (ZMT): Magnetometry data is often collected by walking back and forth in a zig-zag pattern. This can create a striped look. The ZMT filter removes this striping.
  3. De-stagger: If you walked slightly faster in one direction than the other, features might look jagged. The de-stagger tool nudges the data lines to align them properly.

Interpreting the Map

  • Dark areas typically indicate strong positive magnetic signals (e.g., kilns, hearths, iron).
  • Light areas typically indicate strong negative signals.
  • Dipole anomalies (a dark spot right next to a light spot) usually mean buried iron objects.