Archaeological Field Survey - Field Walk (transects)

Field Walk (transects)

Conventionally, fieldwalking in grids or along lines called transects has formed the backbone of archaeological survey fieldwork, at least where visibility is fairly good. A single researcher or team will walk slowly through the target area looking for artifacts or other archaeological indicators on the surface, often recording aspects of the environment at the time. The method 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.

Even with optimal surface conditions the efficacy of fieldwalking varies according longterm land use, topography, weather conditions, the skill and experience of the fieldwalkers, and other factors. Intensive arable agriculture on hilltops will first expose and then pulverize artifacts such as pottery and even chipped stone (typically flint, chert or obsidian) flakes. Conversely, the plateau and upper scarp or valley side soils will move down slope, forming a deep seal over low-lying archaeological deposits, rendering them inaccessible to surface survey. Even artifacts on the surface and with relatively high visibility (i.e., little obscuring vegetation), however, are not consistently detected by surveyors. Consequently, it is unrealistic to expect 100% recovery of artifacts or even sites. We can evaluate surveyors effectiveness at detecting artifacts with "Sweep width," which is the theoretical width of a transect in which the number of artifacts detected outside the sweep is identical to the number missed within the sweep. The poorer the visibility, the poorer the contrast between the artifact "targets" and their surroundings, or the poorer the surveyor's skill or attention, the narrower the sweep width will be.

Modern technology such as GPS has made survey recording much easier, as positions of artifacts or artifact clusters ("sites") can be taken well within the limits limits of accuracy and precision necessary for survey work. Recording the position and attributes of archaeological features has been expedited by customizable portable computing interfaces or mobile Geographical Information Systems (GIS). Databases containing existing regional archaeological data as well as other landscape GIS layers such as soils, vegetation, modern features, and development plans can be loaded on a mobile GIS for referencing, for sampling purposes, and for groundtruth updating directly in the field, resulting a more informed archaeological survey process.

In some areas, the fieldwalking is quite different. When searching in dense forest, artifacts are hidden by a blanket of humus and fallen leaves, and even 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 or feature is hidden below the vegetation, or survey by subsurface testing (SST). SSTs can consist of a series of shovel-test pits dug down below this humus layer or, where substantial later sediments may cover archaeological materials, series of auger or core holes. Because SSTs are much more costly than fieldwalking, surveys by SST usually have very low intensity.