Alison Boulton, Kimberly Gross,

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Alison Boulton, Kimberly Gross, Lindsay Wesner
Archaeogeophysical Exploration
Chapter 8 Page 147-180 Herz/Garrison
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Classes of geophysical methods useful to
archaeological geology

• Seismic reflective/refraction
• Electrical electromagnetic resistivity
  conductivity
• Magnetic
• Radar
• Microgravity
• Thermography

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Seismic

• Introduction of sound into the ground or water at
  sufficient levels to produce a return echo is the
  principle used in seismic reflection and
  refraction.
• Developed for the prospection of petroleum and
  gas deposits.
• Used for archaeological prospection (especially
  detecting underwater sites)
• New seismic systems like CHIRP sonars, which use
  digital processing of the returning signals, can
  produce dramatic increases in the resolution of
  thin sediment layers.
• http//www.youtube.com/watch?vYNkJqJ2VAkQ

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Electric electromagnetic Resistivity/Conductivi
ty

• Electrical methods rely solely on the presence of
  electrical fields E
• Electromagnetic and magnetic methods rely on the
  presence of both electrical fields and magnetic
  fields E H
• Resistivity is the resistance to the electrical
  current determined by the electrical properties
  of the material. Insulators such as glass have
  higher resistance compared to conductors like
  metals which have a lower resistance.
• Conductivity Electromagnetic meter (EM) uses a
  magnetic field to measure the strength of
  electrical permittivity of the soil or rock as a
  function of the induced and measured voltages in
  the coils of the detector.

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Magnetic

• Magnetic devices rely on the fundamental nature
  of the earth, with the metallic nickel-iron core
  in contact with a viscous lower mantel generating
  electrical fields which in turn produce a
  magnetic field.
• The magnitude of the magnetic field observed at
  any point is a function of a features magnetic
  susceptibility, remanent magnetization, size, and
  distance from the measurement device.
• Soils, features, and objects very in their
  ability to be magnetized mostly due to the amount
  of iron present.
• Magnetometer is simply measuring the magnetic
  contrast between an object/feature and its burial
  context.

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Radar

• Ground-penetrating Radar (GPR) is a shallow
  seismic device which uses microwave-frequency
  radar pulses instead of sound.
• Conductivity and frequency largely determine the
  depth of penetration of the radar signal.
• Depends on two properties of soil conductivity
  and the dielectric constant (characterizes the
  relative electrical permittivity)
• http//www.youtube.com/watch?vkjk5l8rbx-A

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Microgravity Thermography

• Microgravity meters measure local variation in
  gravity so that cavities and fill features can be
  referenced to the normal gravity value.
• Thermography units display temperature contrasts
  as a digital image which allow real-time
  visualization of the terrain and buried features.
• Superconducting quantum interference devices
  (SQUIDs) are used in circuits of magnetometers
  and are the most sensitive.
• These devices have been used in geophysics to map
  electrical resistivity in the deep earth. With
  low-energy requirements and enhanced sensitivity
  they can measure small changes in the magnetic
  properties of materials both in the field and the
  lab.