Geophysical methods have been used with increasing frequency in archaeology since 1946; aerial photography has been used since 1919. The geo-physical methods that are most commonly used at present are electrical resistivity, magnetic, and ground-probing radar. Magnetic detectors, particularly when used in a gradient mode or with a continuously recording base station, are used at almost all sites where any geo-physical methods are used. Less commonly used methods include self-potential (sometimes called spontaneous potential), microgravity, radiometric, thermal infrared imagery, and sonic or seismic techniques. Recent developments in image processing and graphic representation have contributed substantially to the archaeologist’s ability to do ”rescue archaeology,” that is, to carry out high-speed, nondestructive reconnaissance surveys for ancient human cultural evidence in advance of modern industrial development.

image050Classical archaeological methods, including trenching with trowels and brushes, require an enormous expenditure of human energy often provided by unpaid student labor. Enthusiasm can provide payment only up to a point, however. Several geo-physical methods are now available that are capable of mapping as much as a quarter hectare of land (at a 1-m grid spacing) in a day’s time. Some conductivity surveys can cover as much as a hectare in a day under special circumstances. Archaeologists often call ground geo-physical methods ”archaeological remote sensing,” or ”archaeo-geophysics.”

The reason for this growth in activity is that geo-physical methods can provide an extremely rapid, three-dimensional reconnaissance of a site, synoptic view of the potential human cultural resources of a target area. Surface geo-physical methods currently in use can usually detect soils disturbed by burials, hollows and voids in structures such as pyramids and ancient fortifications and buried stone foundations. All this can be done rapidly, without ever disturbing the ground. This ability to explore without damaging a site probably does not seem important to a geologist. An archaeologist, however, knows that excavation opens the way for the inevitable destruction of preserved remains by weather and vandals.

Modern examples of the use of geo-physics include searching for hidden cavities in Chephren’s Pyramid at Giza in Egypt (Moussa and Dolphin, 1977), searching for hidden caves in Victorio Peak, New Mexico (Dolphin et al., 1978), and locating buried Olmec basalt monuments in east-central Mexico (Breiner and Coe, 1972). Lost 200year-old graves in Maryland have been found using geo-physical techniques; in one gravesite an iron coffin from the 19th century was identified and dated, and at the same time information was provided on how it was cast (reversed magnetic polarity suggests that it was cast upside down from its final resting configuration; J. Wynn, unpublished data, 1985).

The expertise and techniques available with us for Archaeological Investigations is as follows:

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