logo em-38 inca 2008 international course on archaeogeophysics 20 july-5 august 2008 in İznik,...
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LOGO
EM-38
INCA 2008International Course on ArchaeoGeophysics
20 July-5 August 2008 in İznik, Turkey
Ertan Pekşen
Company Logo www.themegallery.com
Outline
Introduction
Conclusion
EM-38
Data acquisition
Equipment
Interpretation
Theory
Case Study
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Introduction
EM38 has been produced by Geonics. (www.geonics.com)
EM38 is mainly used in agriculture, environmental, archaeology.
EM38 is easy to apply and carry during data acquisitions.
EM-38
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Equipment
EM-38
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Theory
Described by McNeil (1980)
Step 1: An alternating current in the transmitting coil creates a time-varying magnetic field which is sensed by the receiving coil.
Step2: This primary magnetic field (Hp) generates small electric currents in the soil.
Step3: These currents generate a secondary magnetic field (Hs) which is also measured by the receiving coil.
Step 4: The apparent conductivity may be determined from the ratio of the magnetic fields by the relationship.
EM-38
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Data acquisition
44
2211
33
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EM-38 specifications
Frequency= 14.6 kHz
T-R distance=1 m
Horizontal and vertical dipoles
EM-38
h=0.75mh=0.75m h= 1.5mh= 1.5m
Effective depth rangesEffective depth ranges
Measured quantities:Measured quantities:1)1) Apparent conductivities (mS/m)Apparent conductivities (mS/m)2)2) In phase ratio of the secondary to primary In phase ratio of the secondary to primary
magnetic field in parts per thousand (ppt)magnetic field in parts per thousand (ppt)
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EM38 Apparent Conductivity
Fixed frequency: f=14.6 kHz
Fixed coil spacing: s=1 m
Apparent conductivity (B=s/ << 1):
Hp primary field
Hs secondary field
skin depthp
s
0
a H
H
s μ f π
2σ
2
EM-38
2
0σω
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Interpretation
EM-38
**Apparent conductivity map since the Apparent conductivity map since the depth range is very shallow.depth range is very shallow.
**Forward and Inverse modeling Forward and Inverse modeling (Hilgendorf, 1997) and (Deidda et (Hilgendorf, 1997) and (Deidda et al., 2003)al., 2003)
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Case Study (Simpson et al 2008)
EM-38
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…continued
EM38
EM38DD provides simultaneous measurement of both (vertical and horizontal) dipoles at
all times.
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Case Study
EM-38
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Conclusion
EM-38
EM38 can be applied to archealogy.
EM38 can quickly be carried out on a field.
EM38 provides information about underground no more than 1.5 m depth .
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