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Modern archeology: major techniques used for the future site location

   There are a number of methods used for identification of the archeological sites. This paper is going to discuss most important ones implied these days. They are: metal detectors, techniques of grounds survey and geological surveys.

   For instance geological survey is conducted with the help of various approaches. The two main ones are resistivity and magnetometry. Magnetometry involves the use of magnetometers, which detect differences in the soil indicated by changes in its magnetic field.

   There are two instruments that can be used in the process: Data from proton gradiometers and proton magnetometers. Readings from gradiometers are the easier of the two to process; they record the readings between two separate detector bottles at either end of a pole held upright by the archaeologist. Inconsistencies in the earth magnetic field under the surface affect the lower of the bottles.

   Proton magnetometers take readings of the absolute magnetic field at set points on a grid, rather than the difference recorded between the bottles. Heating to about seven hundred degrees Celsius, by kilns or furnaces etc cause the random alignment of magnetic particles to retain the alignment of the earth magnetic field at the time of cooling, or passing the Curie point. It is this course of action that is used to date pottery. The process is not an intrusive one, as the magnetometer is carried along a grid by the archaeologist. It is also relatively quick to conduct, although the data still require processing. For this reason, it is preferred to resistivity when conditions are favourable. Once the readings have been taken, they are converted into a map of the area being surveyed. The map will illustrate any magnetic differences in the form of either a contour map or distinct shading. 

   When using magnetometers, it is critical that the operator has no ferrous metal on their person. This includes metal zips, jewellery, shoelace eyelets and even certain metal surgical implants. The reason for this is that the readings are affected by the presence of metals so data can be inaccurate. The resistivity of the area being surveyed concerns the measurement of electrical resistance encountered below the surface. The twin electrode is the most useful instrument for testing resistivity. It is a frame containing a meter, batteries (to provide power) and two probes, usually half a metre apart, but this distance can be altered when a deeper survey is required. Two remote probes and a connecting cable are also necessary; this links the probes when placed at least thirty times the distance between the static probes. For example, if the primary, or static probes on the frame were one metre apart (in the instance of a deep survey) the remote probes would need to be placed a minimum of thirty meters from the area under investigation. It is this that makes the process more complicated than other methods, such as magnetometry. The most accurate results can be obtained in the summer months, in the case of temperate climates, as the soil moisture content is lower then, so the equipment can detect differences in resistance more easily.

   An electrical current is passed through the ground between the two electrodes in order to measure the resistance. It is more difficult for the current to pass through drier, more compact material, such as a buried wall of a house or an ancient road than it would be for it to pass through damp clay soil, which it would penetrate relatively easily. The data collected is entered into a computer programme that produces an image of the land being surveyed. This image will indicate the presence of archaeological artefacts by shading them differently to the rest of the soil. More modern resistivity testing equipment will produce more accurate and detailed images, but this is expensive, and often not financially viable.

   Polarisation is a common condition encountered whilst testing resistivity of a survey area. This produces erroneous reading, and to prevent its occurrence, four probes are required. For Ground Survey's to be conducted, again there are a variety of data collection techniques that archaeologists can use. The most advanced being Topography, but equally important are the less complicated methods of Planning and Mapping.  Topography involves the recording of the surface character of an area. A theodolite is used to take readings of the ground, which are entered into a computer programme that then creates a 3D image of the site surface. It is often used with geophysical survey techniques to amalgamate the site surface image, with the sub-surface one.  Planning and Mapping techniques are used to create a plan of the archaeological site. This plan can be scaled correctly so the accurate location if the archaeological features of interest can be determined by the entry of the data into a mapping package on a computer. 

   Metal detectors are useful pieces of equipment used by archaeologists. The distance into the earth's surface that they can penetrate limits many metal detectors. They are not usually necessary if the area being  surveyed has already been surveyed by a magnetometer, as they too would detect the presence of any metal located beneath the surface. The metal detectors send impulses down into the ground, and when they hit a metal object, they bounce back up and activate a bleeper to alert the operator of hidden metal.

   The use of metal detectors by amateur archaeologists has in the past proven to be very useful in the discovery of sites possessing a wealth of archaeological artefacts. Once alerted to the presence of metal beneath the soil, professional archaeologists can use some of the site location techniques to determine the relevance of the finds, and where appropriate conduct excavations, which can often lead to the discovery of great archaeology. All too often though, metal detectors can give positive readings when the metal prompting such readings are simply old cans or other man made waste.

Bibliography:

1. Carke, A 1990 Seeing beneath the soil: Prospecting methods in Archaology.

2. Greene, K 1996 Archaeology, An Introduction.

3. Scollar, I Tabbagh, A (et al) 1984 Archaeological Prospecting and Remote Sensing.

4. Renfrew, C & Bahn, P 1997 Archaeology: theories, Methods and Practice (85-97).

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