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Archaeological Prospecting

Archaeological Prospecting. What have you got? Where do you look? Where do you dig??? *Aerial photography *Electrical resistivity *Magnetometry *Ground penetrating radar (GPR) Electromagnetic induction Seismic probes (sonar) Gravimetry Gamma “radiography” IR emission imagery.

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Archaeological Prospecting

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  1. Archaeological Prospecting • What have you got? • Where do you look? • Where do you dig??? • *Aerial photography • *Electrical resistivity • *Magnetometry • *Ground penetrating radar (GPR) • Electromagnetic induction • Seismic probes (sonar) • Gravimetry • Gamma “radiography” • IR emission imagery Archaeology without a shovel

  2. What are the clues? Shadowing

  3. Soil marking Filled ditches- More moisture Roman roads- Paving-less moisture

  4. Crop or vegetation marking Roman villa

  5. Familiar territory

  6. Less familiar

  7. Zoom out

  8. What is it? Nazca, Peru 200 BCE-600 CE Rocks removed to reveal lighter colored subsoil No rhyme or reason to complex array of lines photo

  9. Aerial photo-hummingbird

  10. Spider

  11. Sketches of others

  12. Geometric patterns

  13. Kerkenes, Turkey: ~585-545 BCE

  14. Kerkenes-aerial view

  15. Closer aerial photo-interior

  16. How to see without digging? • Want to use electrical conductivity: • Good insulators–dry brick, non-porous stone, glass, voids, dry soil • Good conductors–metals • In between (a tremendous range)–moist brick or soil, water • A way to measure conductivity of what’s underground??? Activities of man-----subsurface inhomogeneities

  17. Currents in homogeneous soil _ +

  18. = local high conductivity _ +

  19. Where is it? _ _ _ + + +

  20. How deep is it?? + + _ _ Sensitive to depths ~ 1.5 x separation

  21. What do you see? =???? • Higher conductivity • Higher moisture content • More dissolved minerals • Metal artifacts • Lower conductivity • Lower moisture • Masonry • Voids

  22. Conductivity array

  23. Conductivity data 20 meter grid

  24. Magnetometry • How to look for magnetic materials? • Simplest of magnetometers is a compass

  25. Magnetometry Signal Magnetometer Buried object Earth’s field Surface

  26. Magnetic gradiometer Difference Signal Gradiometer difference Buried object Earth’s field Surface

  27. Magnetometry Sense variations in Earth’s magnetic field need high sensitivity killed by fluctuations in time Solution: magnetic gradiometer pair of sensors look only at difference Sensitivity of the best (not the one illustrated): 10-8 of Earth’s field!

  28. What do you see? Local variation in magnetism • Most obvious–iron artifacts • Recall colors of unglazed pottery • Red–hematite–Fe2O3–non-magnetic–“oxidized” • Black–magnetite–Fe3O4–magnetic–“reduced” • Magnetite containing soil • Soil replaced by stone masonry or red brick • Ditch or earthworks filled in by non-magnetic soil • Alignment of grains in clays disturbed by working • Soil disturbed (e.g., a grave) allowing oxygen access • Hematite containing soil • Reduction of iron in fire hearth • Destruction of building by major fire

  29. 6-element gradiometer

  30. Real data Conductivity Magnetometry

  31. Columned hall

  32. Aerial photo

  33. 100meters Magnetic survey

  34. Ground Penetrating Radar = GPR • How did we see below the surface of a painting? • Used Infra-red light to penetrate surface layer and see how it interacts with deeper layers. • Radar uses “light” of MUCH longer wavelength to penetrate soil.

  35. Electromagnetic waves

  36. Radar Distance = (travel time)/(twice velocity of light) 10 microseconds  1 mile 2 nanoseconds  1 foot

  37. Can energy really go from here to there???

  38. WE SUGGEST THAT YOU TURN OFF YOUR LAPTOPS AND WIRELESS DEVICES (INCLUDING CELL PHONES)

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