2. 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

3. What are the clues? Shadowing

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

5. Crop or vegetation marking Roman villa

6. Familiar territory

7. Less familiar

8. Zoom out

9. 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

10. Aerial photo-hummingbird

11. Spider

12. Sketches of others

13. Geometric patterns

14. Kerkenes, Turkey: ~585-545 BCE

15. Kerkenes-aerial view

16. Closer aerial photo-interior

17. 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

18. Currents in homogeneous soil _ +

19. = local high conductivity _ +

20. Where is it? _ _ _ + + +

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

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

23. Conductivity array

24. Conductivity data 20 meter grid

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

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

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

29. 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!

30. 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

31. 6-element gradiometer

32. Real data Conductivity Magnetometry

33. Columned hall

34. Aerial photo

35. 100meters Magnetic survey

36. 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.

37. Electromagnetic waves

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

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

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