Digital stratigraphic recording and 3D laser scanners

Archaeology has, over the course of its history, developed from purely find oriented to context oriented excavation process. One of the most important recognition of the last centuries, that changed archaeological research, was the fact that any archaeological site is stratified. And any archaeological stratification is unique. The stratigraphic excavation method makes it possible to record the single units of the stratification (i.e. deposits and surfaces) along with all its attributes and relations, and to create from this data, a stratigraphic sequence.
The creation of this stratigraphic sequence (Harris matrix) from the deposits and single surfaces, transformed into unique numbers, is totally independent of the finds contained in the excavated mass. The analysis of the finds (i.e. all relevant material remains within the archaeological stratification) and the single units of stratification, after the excavation, allows for a phasing (structural) and periodisation (chronological) to be created out of the stratigraphic sequence. This sequence of phases or periods adds a structural and chronological grouping. A period interface can be understood as a surface composed by the recorded single surfaces or only parts of them, as they were exposed to air during a specific time span of use, on top of older deposits that are in disuse. This further subdivision does not however change the original stratigraphic sequence, instead merely presents an interpretative summary, marking out structural or chronological aspects.
Single deposits are 3D volumes that are destroyed by excavating them in the reverse order of their deposition. The data from deposits, the material aspects of stratification, can only be captured by sampling. The deposit, is reduced to a unique number in the stratigraphic sequence and imparts that number to all of the portable finds and samples found within its volume upon its destruction. The finds and samples are recorded in 3D space as 3D points or small volumes, thus reduced to a set of coordinates. All further data derived from the finds can be stored in a database, photographs and drawings.
Contrary to deposits, surfaces, the immaterial aspects of stratification, can be recorded entirely. Single-surface recording provides the ability to virtually reconstruct the excavated volume in three dimensions. Therefore, 3D recording of the top and the bottom surface of any single deposit is necessary to fully reconstruct the part of the site destroyed by excavation. The recording of a single-surface can be done by documenting its boundary polygon and its topography, thus is reduced to a set of coordinates as well. The outstanding importance of 3D single-surface recording for the stratigraphic record encourages the use of high resolution 3D laser scanners combined with digital imagery as a standard instrumentation for future archaeological research. They provide highest accuracy for the documentation of stratigraphic surfaces.
The collected sets of coordinates from surfaces and deposits are the primary raw data for a GIS providing the ability to visualize surfaces as contour plots or triangulated irregular networks, to combine the boundary outlines with rectified digital images of the deposits and to map registered find spots within the volumes, classified by stratigraphic position or material aspects. GIS functionality permits dynamical mapping of single surfaces or the creation of composite maps (phase or period maps, sections at any position, etc.), based on the recorded data. The decisions on how to compose the necessary maps is derived from the analysis of the stratigraphic sequence. The secondary data dealing with the various aspects (location, material, date etc.) of the finds uncovered is stored as well in the spatial database of the GIS and can be combined with the graphical visualisations to be analysed and counterchecked.