Author : Sharon White
Geological Survey involves the use of a variety of methods and techniques to produce a detailed map of what is below the surface of the area being surveyed. The primary techniques are Magnetometry and Resistivity. Geophysical survey techniques are the most commonly used method of site identification when a suspected archaeological site lies beneath the land surface. They are non-intrusive and are subsequently invaluable when excavation is not possible.
Before conducting either a Geological Survey, or a Ground Survey, a grid needs to be created for the area under investigation. Control points are established which allow the site to be synchronized with the National Grid. First of all, a Baseline is established in the prevailing direction of the site. The ends of this are co-ordinated by Triangulation. This fixes the baseline to the surround area, usually by using tape, which is then broken up into suitable units marked by stakes placed in the ground. Once this has been completed points perpendicular to the baseline are set up, again using tapes. In large areas, Pythagorean theory is implemented (A2 + B2 = C2) but when the area being surveyed is smaller, the Pythagorean triangle system is best. All the corners angles of the grid must be at 90 (a square) so the square root of the two sides of the triangle can be calculated, a measurement necessary to determine the hypotenuse of the right angle triangle. The measurements are then used, once the tapes are situated at the two ends of the baseline (often referred to as A and B) so each square can accurately be constructed.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.The article was produced by the member of masterpapers.com.
Sharon White is a senior writer and writers consultant at term papers. Get some useful tips for thesis and buy term papers .
Keyword : archaeological, techniques, efficiency
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