Transcript Magnetics, Radar, and Resistivity

Archaeological Geophysics – a quick look
Magnetics, Radar, and Resistivity
Steve Sheriff
Professor of Geophysics
University of Montana – Missoula
www.umt.edu/geosciences
www.umt.edu/geosciences
Bar magnetic and iron filings
Earth’s magnetic field
Total Field Magnetics
Magnetics exploits changes in subsurface magnetic properties:
• measure subtle changes in Earth’s magnetic field at the surface
• map those changes
• Interpret the results
The best all round tool for
archaeological investigation
Use for large area
Use other tools on smaller
areas outlined by magnetic
anomalies
Ground Penetrating Radar – echoes off reflectors
Ground Penetrating Radar
GPR relies on radar waves
reflecting off subsurface
layers and objects
Transmit & receive radar
waves (200 MHz - 1000
MHZ)
Make profiles and maps of
the reflectors
Electrical Resistivity
• measures the ability of the subsurface to transmit electricity
• we put electrodes in the ground, connect them to a power source, and
measure the result
Sand Hill Cemetery served the mining towns of Coloma and Garnet
Electrical Resistivity
Sand Hill Cemetery between the mining towns of Coloma and Garnet
Syscal Kid 24 DC
resistivity switch
Electrodes & cabling
Congress would be proud: we found graves under tombstones!
Electrical resistivity over a
suspected burial site near
Coloma, MT
Cinnabar, the historic entrance
to Yellowstone National Park
S.D. Sheriff, D.MacDonald, D.Dick, 2010,
Decorrugation, Edge Detection, and Modeling of
Total Field Magnetic Observations from a Historic
Town Site, Yellowstone National Park, USA.
Archaeological Prospection, V. 17, p.49-60.
Magnetics
yields maps
and subsurface
models
enhance and
look for nonnatural features
Inverting for the subsurface shape yields
‘best estimates’ for the distribution of
magnetization causing the observations
Total Field Magnetic, Radar, and Archaeological Studies on the Shores of
Yellowstone Lake, Yellowstone National Park, USA
Magnetic surveying
results in maps and
subsurface models
Radar yields 3D
volumes with both
profiles and timeslice maps
• TU 1 yielded a fire hearth dating to 1720±40 B.P. (Beta-265305), as well as abundant
evidence of obsidian stone tool manufacture
• TUs 2, 3, and 4 yielded only boulders. We excavated these, despite each individual anomaly
having the character of a boulder with remanent magnetization, because their concentration
and alignment was promising. In a nearby area with similar analysis one such buried boulder
turned out to be a long-term bench for flaking and other cultural activities.
• At about 0.8 meters below ground surface, TU 5 contained a fire hearth dating to 2920±40
B.P. (Beta-265306).
• TU 6 contained a rock concentration (likely a hearth) dated at 3,100±40 B.P. (Beta-265307).
Total Field Magnetics
Radially distributed features
around the center anomaly from
an obsidian boulder at one meter
The boulder was a long term seat
for flaking
The magnetic signature of the
boulder has been attenuated to
highlight the surrounding features
Radial magnetic highs around an obsidian boulder one meter below the surface
(center anomaly) are almost certainly cultural features – the boulder was a long
term seat for flaking
Northeastern Washington
Magnetics
Before:
After:
rectilinear
footprints are most
likely cultural
features
Where are the boundaries of this cemetery?
What was the layout
of this 1800’s mining
town?
Serendipity – 4” cast
iron pipe!
Missoula
IDAHO - GPR
Here’s one I’m
excited about:
~ 75 cm deep
~6-8 m diameters
The old road is
shallower and not
apparent on the
surface
WWII Hospital Trenches in the Philippines
S.D. Sheriff, D.MacDonald, D.Dick, 2010, Decorrugation, Edge Detection, and Modeling of Total Field
Magnetic Observations from a Historic Town Site, Yellowstone National Park, USA. Archaeological
Prospection, V. 17, p.49-60.
S.D. Sheriff, D.MacDonald, 2010, Total Field Magnetic, Radar, and Archaeological Studies on the Shores of
Yellowstone Lake, Yellowstone National Park, USA. International Society of Archaeological Prospection
(ISAP), v. 23, April 2010, p.3-5.
S.D. Sheriff, 2010, Matched Filter Separation of Magnetic Anomalies Caused by Scattered Surface Debris at
Archaeological Sites. Near Surface Geophysics, v. 8, #2, p. 145-150.
S.D. Sheriff and P.T. Doughty, 2009, Magnetic and Radar Investigations of Site 45CH703, Tumwater Canyon,
Washington. Report (not refereed) prepared for Archaeological and historical Services, Eastern Washington
University, 46 p.
S.D. Sheriff and G. Carlson, 2009, Total Field Magnetometry and Ground Penetrating Radar Investigations at
Kelly Forks Work Center, Clearwater National Forest, Idaho. Report (not refereed) prepared for USFS
Clearwater National Forest, 32 p.
S.D. Sheriff, 2009, Archaeological Scale Magnetic and Radar Investigations at Northwestern Yellowstone
Lake, Yellowstone national Park, USA. Report (not refereed) presented to Yellowstone National Park Center
for Resources, Yellowstone National Park, USA, 41 p.
S.D. Sheriff, 2009, Archaeological Scale magnetic, Electrical, and Radar Investigations at Boundary,
Washington, LPOE, USA. Report (not refereed) prepared for Historical Research Associates, Inc., Missoula,
MT, USA, 46 p.
Schmidt, R., Crossland, N., Ballas, M., McKeown, and Sheriff, S., 2008, Remote Sensing of Pineview Park
Missoula Montana. Student Project Report (not refereed) completed for Missoula Parks & Recreation
Department, Missoula, Montana.