The Poulton Research Project

Topographic Survey (so-called here to distinguish it from Geophysical Survey) can be broadly defined as "the technique and science of accurately determining the terrestrial or three-dimensional space position of points and the distances and angles between them". At Poulton the Survey team uses these techniques to:

Determine the positions of points of archaeological interest, including trenches, finds, features, skeletons, etc.
Measure these positions in three dimensions, horizontally (East and North) and vertically (height).
Relate the positions of these objects to each other, to the wider landscape, and to the Ordnance Survey National Grid.
Set out grids at regular intervals (usually 5 or 10m), as an aid to drawing detailed plans, for geophysical measurements or for topographical surveys.
Relocate objects which are no longer visible, e.g. trenches which have been backfilled.

Levelling

Levelling is a simple technique that is used to determine the heights of points above Mean Sea Level (MSL).

Total Station

A Total Station is an electronic theodolite combined with an electronic distance measurement (EDM) instrument. By measuring distances and angles to a special optical target, it allows us to compute the plan positions and heights of points.

The Total Station we use at Poulton is a fairly basic model (it's all we can afford!), which can measure angles with an accuracy of about 20 seconds of arc, and distances up to 500 metres with an accuracy of 5mm + 5ppm. This translates into positional accuracies of a few cm, and is more than adequate for archaeological purposes.

Global Positioning System (GPS)

The GPS equipment normally used by surveyors (as seen, for example, on Time Team), is very accurate but far too expensive for Poulton! Low-cost GPS receivers of the type used for navigation normally achieve a positioning accuracy of around 10 metres, which is inadequate for survey work. However, by collecting data for 30 minutes and processing it later with data simultaneously collected at a known point (e.g. Daresbury), we can compute the National Grid coordinates of a point to within about 20 cm. Based on this, we have generated formulae which allow us to transform co-ordinates from the local site grid into National Grid and vice-versa.

3-D Model from Earthworks Survey (between Ring Ditch and Chapel)

Detailed Survey of the Ring Ditch

References

A formal report on the establishment of the Poulton Survey Control Network and the determination of the relationship between the local and National Grids (PDF, 657 kbytes).
"Where on Earth are We?" - a report from English Heritage on the use of the Global Positioning System in archaeological field survey (PDF, 1.8 Mbytes).
"With Alidade and Tape" - a report from English Heritage on graphical and plane table survey of archaeological earthworks. Particularly useful where electronic equipment is not available (PDF, 1.5 Mbytes).