1. Active Remote Sensing for Archaeology
Surface and subsurface clues

2. Radar Image – Lost city of Ubar on the Arabian Peninsula (Omam)
Occupied from 2000 BC to 300 AD. Remote desert outpost where traders assembled caravans for transporting frankincense.
Dunes
Wadi (stream bed)
Ubar
Trails leading to Ubar
Limestone bedrock
This Radar image uses 2 bands with 3 polarizations to make a color image. Used to find Ubar in 1992

4. Great Wall of China

5. Applications of radar for archaeology
Characterization of surface can yield archaeological information not apparent in optical imagery
Surface roughness can relate to past activities
Ability to see through clouds (e.g., tropics)
Ability to see through tree canopies (e.g., tropical forest)
Radar can penetrate into dry soil and detect subsurface features
Airborne – a few cm to a couple of meters
Ground penetrating radar – a few meters to 50 m

6. Airborne imaging radar for archaeology
Airborne radar can survey large areas quickly
Creation of detailed topographic data that can reveal archaeological features (e.g., pyramids, temples, burial mounds)
Can penetrate slightly into the surface and see buried walls, etc.
Can penetrate tropical forest canopies and clouds (e.g., Inca ruins in Peruvian jungles)
Can sense surface differences associated with trails and roads that aren’t spectrally visible

7. Case Study: Angkor Wat, Cambodia
Complex of 60 temples that date to 9th century
Once had population of 1 million
Today is buried in dense rainforest
Usually cloudy
Scientists used Shuttle Imaging Radar to map this site, including unexcavated structural remains

9. Ground Penetrating Radar (GPR)
Long wavelength radar can penetrate into dry soil
Large dielectric constant of water inhibits penetration into wet soil
Works particularly well in dry sand
Physical and chemical changes in the ground affect radar returns and can give clues about buried materials
Wherever there is a change in the dielectric constant of materials the radar is reflected.
Strongest reflection where materials very different.
Thanks to Lawrence Conyers, University of Denver ( for much of the GPR info in this lecture!!

10. Why GPR for Archaeological Surveying?
GPR data are inexpensive and easy to acquire.
GPR is non-invasive, leaving archaeological artefacts intact.
GPR has the potential to image the subsurface with a higher resolution than any other geophysical technique.
It’s a valuable part of a geophysical dataset – excavation can be completely avoided if enough high quality are collected.
Slide and photo from Adam Booth, Leeds University, England

12. How do you collect GPR data?
Radar instrument is moved along closely spaced transects
Radar returns are measured every 2 – 10 cm
Can plot strength of return with time for round trip on y-axis
Plotting all traces on one graph and coloring strong returns darker and weak returns lighter give a “picture” of the subsurface

13. GPR data collection at Petra, Jordan
(Photo by Dr. Lawrence Conyers)

15. Trade-offs
Long wavelength radar can penetrate more deeply into the soil but…
Long wavelength radar has low spatial resolution (can only sense large objects)
Minimum object size that can be detected is about 75% of wavelength
So…have to strike a balance between penetration depth and resolution
Also must consider the radar “footprint” when planning transect spacing so that all objects are illuminated by the radar pulses

16. Kansas Cemetery
Black squares are tombstones
Colored areas are graves

17. Civil War Bunkhouse – Ft. Garland, Colorado

18. Soil moisture can have strong affect
Kiva before and after rain – rain obscures ability to see the structure
Figures from Lawrence Conyers

19. Kiva-like structure, Grand Gulch, Utah

20. References
L.B. Conyers and D. Goodman, 'Ground Penetrating Radar, An Introduction for Archaeologists' (AltaMira Press, 1997)