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Most geophysical survey techniques involve the computer. Maps are produced which display the consequence of their moisture content. Buried
use of instruments which work in one of two ways. locations of the features. foundations and stone walls may be more resis-
Either they measure distortions of the earth’s tant to an electrical current while ditches, pits, and
magnetic field created by buried features such as Electrical resistance transmits a low voltage cur- metals more easily conduct.
hearths, pits, and house floors, or they pass vari- rent into the soil via inserted metal probes. The
ous kinds of energy through the ground in order to ability of buried materials to resist the electrical Conductivity. Although conductivity instruments
detect such features. The data are collected with current provides the basis for resistivity survey. are generally less sensitive than resistance meters
the instruments and then transferred to a portable Buried materials resist electricity generally as a to the same phenomena, they do have a number
of unique properties. For one, they do not require
University of Iowa Office of the State Archaeologist direct contact with the ground and, hence, can
be used in conditions unfavorable to resistance
meters. They also have greater speed, and unlike
resistance instruments, can respond strongly
to metal—a disadvantage when a site contains
extraneous metal items not related to the original
inhabitants.
Magnetic gradiometry. Buried materials often
produce slight distortions of the earth’s magnetic
field. These distortions appear as “hot spots” or
anomalies detectable with an instrument known
as a magnetometer or gradiometer. After establish-
ing a grid of transects at a site, the archaeologist
passes the magnetometer over the surface obtain-
ing measurements at regular intervals.
Magnetic susceptibility. Iron minerals within the
soil can be altered through biological decay and
burning which can enhance the magnetic suscep-
tibility of the soil. Field equipment can be used
to measure the magnetic susceptibility allowing
zones to be mapped which may indicate areas of
potential archaeological activity.
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