Archaeological field survey is the methodological process by which archaeologists (often landscape archaeologists) collect information about the location, distribution and organisation of past human cultures across a large area (e.g. typically in excess of one hectare, and quite often in excess of many sq. km). It may be: (a) intrusive or non-intrusive, depending on the needs of the survey team (and the risk of destroying archaeological evidence if intrusive methods are used) and; (b) extensive or intensive depending on the types of research questions being asked of the landscape in question. Surveys can be a practical way to decide whether or not to carry out an excavation (as a way of recording the basic details of a possible site) and may also be ends in themselves, as they produce important information about past human activities in a regional context.
A special type of field survey is the rescue survey, used when an area of possible archaeological importance is under threat. This is usually connected to construction work, and is undertaken to decide whether an excavation is necessary or not before work can commence on the site.
Archaeologists use a variety of tools in survey, including GIS, GPS, remote sensing, geophysical survey and aerial photography.
Research and planning: A field survey is usually the result of a long period of research and planning. The process will normally start with the notion that an area is worth further investigation, or that a site requires excavation (or that it should at least be recorded in some way).
Rationale: There are several reasons that an area may be considered to be worth surveying. In no particular order, they are:
- Artifacts found: Locals have picked up artifacts, sometimes found in the local museum but more often in private homes or old buildings such as churches, and it is unclear where they are coming from.
- Literary sources: Old literary sources, in some cases ancient Roman or Greek texts, have provided archaeologists with clues about settlement locations that have not been archaeologically documented. Sometimes the texts may be quite recent; a book on local history that mentions an interesting area.
- Oral sources: In many locations, local stories contain some hint of a greater past, and there is often some truth to them. It is not uncommon for someone to remember that a grandfather who used to walk the hills around a town as a shepherd used to talk about columns from an old temple, without having actually seen these themselves.
- Local knowledge: In many cases, locals actually know where to find something that is of interest to archaeologists. They may not have reported it, either because it’s simply a part of their world, or because they fear intrusions on their land.
- Previous surveys: In some places, a survey was carried out in the past, and is recorded in an obscure academic journal. It may have been disregarded at the time, but more recent technologies and finds from other sites might cast a different light on it.
- Previous excavations: Excavations carried out before the middle of the 20th century are notoriously poorly documented. They were also often carried out in a way that left much of the evidence the modern-day archaeologist is looking for behind, preferring to carry away only fine pottery, jewelry and statues.
- Lack of knowledge: Many areas of the world have little known about the nature and organisation of past human activity at the regional level (even when one or more ‘sites’ may be known from an area, often little is known about the wider distribution of contemporary settlements, and how settlement patterns may change over time). Archaeological field survey is the primary tool for discovering information about previously uninvestigated areas.
Aerial photography: Aerial photography is a very good tool when planning a survey. Remains of older buildings often show in fields as cropmarks, as they are often just below the topsoil and therefore affect the crops or grass. There should preferably be photographs of the same area at different times of the year, allowing the analyst to find the best time to see cropmarks.
Previous work on the site: If the indicator that started the process was not a record of previous work, the archaeologists will need to check if any work has been done. As many older surveys and excavations were published in papers that were not widely spread, this may be a difficult task. A common way to handle this is through a visit to the area, to check with local museums, historians and older people who might remember something.
Permissions: It is usually a simple matter to gain permission to perform a survey, especially a non-intrusive one. If the area is privately owned, the local laws may or may not require the landowners’ co-operation. Permission for an intrusive form of survey may be more difficult to acquire, due to the fear of destroying evidence.
Intrusive vs. non-intrusive surveys: In a non-intrusive survey, nothing is touched, just recorded. An intrusive survey can mean different things. In some cases, all artifacts of archaeological value are collected. This is often the case if it is a rescue survey, but less common in a regular survey.
Another form of intrusive research is bore holes. Small holes are drilled into the ground, most often with hand-powered bores. The contents are examined to determine the depths at which one might find cultural layers, and where one might expect to strike virgin soil. This can be valuable in determining the cost of an excavation – if there is a build-up of several meters of soil above the layers the archaeologist is interested in, the price will obviously be much higher than if artifacts are found only centimeters below ground.
Extensive vs. intensive survey: Archaeological field survey can be divided into two types: intensive survey and extensive survey. The former is characterised by the complete or near-complete coverage of the survey area at a high-resolution, most often by having teams of survey archaeologists walk in a systematic way (e.g. in transects) over parcels of the landscape in question, documenting archaeological data such as lithics, ceramics and/or building remains. Extensive survey, on the other hand, is characterised by a low-resolution approach in which (e.g.) only samples of a larger study area (often in excess of several sq km) are visited. Extensive surveys are quite often designed to target the identification of archaeological sites across a large area, whereas intensive surveys are designed to provide a more comprehensive picture of the location of sites and the nature of off-site data (e.g. field systems, isolated finds, etc.). Intensive survey is the more costly, timely, and ultimately informative of the two approaches, although extensive survey can provide important information about previously unknown areas.
Field walk: An important part of the survey is normally the field walk (or transect). The common way to perform it is to construct a grid, place the survey team on a line and then walk slowly through the area looking for artifacts or other indications. This works best on either ploughed ground or surfaces with little vegetation. On ploughed surfaces, as the soil is turned regularly artifacts will move to the top. Erosion and soil loss on uncultivated and lightly vegetated soil (e.g., in semi-arid environments) may cause artifacts to also ‘rise’ to the surface.
Modern technology such as GPS has made survery recording much easier, as positions can be taken well within the limits necessary for survey work.
In some areas, the field walk is quite different. When searching in dense jungle, buildings may be covered by vegetation, and are therefore virtually invisible even at short distances. The team will then need to look for unnatural changes in the vegetation and landscape to decide if a building is hidden below the vegetation.
Narrowing it down: At this stage, the problem is often that one knows the approximate distribution of archaeological material, but it needs to be more precisely mapped. During the field walk, the members of the team are likely to miss minor pieces of artifacts hidden in vegetation. However, if they are all trained to look for the same thing, it is likely that they will miss the same amount of artifacts, and the results of the survey can therefore still be used to draw a map of find frequencies within the grid system. This might in turn make it possible to identify an archaeological site.
Geophysical survey: Geophysical survey is used for subsurface mapping of archaeological sites. In recent years, there have been great advances in this field, and it is becoming an increasingly useful and cost-effective tool in archaeology. Geophysical instruments can detect buried archaeological features when their electrical or magnetic properties contrast measurably with their surroundings. In some cases individual artifacts , especially metal, may be detected as well. Readings taken in a systematic pattern become a dataset that can be rendered as image maps. Survey results can be used to guide excavation and to give archaeologists insight into the patterning of non-excavated parts of the site. Unlike other archaeological methods, geophysical survey is not invasive or destructive. For this reason, it is often used where preservation (rather than excavation) is the goal.
The geophysical methods most commonly applied to archaeology are magnetometers, electrical resistance meters, ground-penetrating radar (GPR) and electromagnetic (EM) conductivity. These methods provide excellent resolution of many types of archaeological features, and are capable of high sample density surveys of very large areas and of operating under a wide range of conditions. While common metal detectors are geophysical sensors, they are not capable of generating high-resolution imagery. Other established and emerging technologies are also finding use in archaeological applications.
Although Geophysical survey has been used in the past with intermittent success, good results are very likely when it is applied appropriately. It is most useful when it is used in a well-integrated research design where interpretations can be tested and refined. Interpretation requires a knowledge both of the archaeological record, and of the way it is expressed geophysically. Appropriate instrumentation, survey design, and data processing are essential for success, and must be adapted to the unique geology and archaeological record of each site. In the field, control of data quality and spatial accuracy are critical.
Analysis: The most important part of the survey is the analysis. The types of questions typically asked of survey data include: what is the evidence for first occupation of an area; when was this area occupied; how are sites distributed; where are sites located; what evidence is there for a settlement hierarchy; what sites are contemporary with each other; how has the modern landscape interfered with the visibility of archaeological remains; what sorts of activities can be recognised (e.g. dwellings, tombs, field systems); how many people lived in this area (at any given time); why did people choose to live in this area; how has the landscape changed over time; what changes in settlement patterns have there been?
At times, one part of the survey may not have yielded the evidence one wanted to find. For instance, very little may have been found during a field walk, but there are strong indications from geophysical survey and local stories that there is a building underneath a field. In such a case, the only way to decide if an excavation is worth the cost is to carefully analyze the evidence to determine which part to trust. On the one hand, the geophysics might just show an old and forgotten waterpipe, but it might also show the wall of just the building the archaeologists were looking for.
The analysis therefore includes careful examination of all the evidence collected. A method often used to determine its value is to compare it to sites of the same period. As the number of well-documented surveys grow, this becomes a slightly easier task, as it sometimes is easier to compare two survey results that a survey result and an excavated site. [GFDL Source & Copyright]