Window sampling is a method of extracting a column of soil from the ground without disturbing it. The sampler collects one-metre length samples of soil (tubes). After each tube is extracted, the sampler is returned to the borehole for the next metre, 0-1m, 1-2m, 2-3m and so on, up to a depth of six metres. (Greater depths can be achieved, up to 10 metres in suitable ground conditions) The tubes are sealed, and taken back to the laboratory, or opened on site for analysis. The position and height above Ordnance datum of each borehole is recorded in three dimensions.
Back in the lab, tubes are opened and examined for details about the soil throughout the full length of the borehole, and the location of any artefacts is noted. Distinct layers are noted and the exact position and depth of the top and bottom of each record electronically.
On small sites, layers can be matched between boreholes, and large features such as defensive ditches or landscaping can be detected, while for large areas, layers of similar date can be matched up to show former land surfaces.