Survey and Geomatics

Introduction
Archaeology South-East offers a full archaeological earthwork and landscape surveying service carried out by a professional team of archaeologists and land surveyors. We have invested in some of the most up to date land survey equipment available on the market.

We are also able to offer our own detailed geophysical surveys and other field survey techniques that can be combined with our land survey results to provide the client with a deep understanding of the archaeological landscape; this will enable them to make informed choices about where to locate any further archaeological investigations, such as evaluation trenches or targeted area excavations. We are able to offer this service both in Britain and abroad. We can also manipulate and manage our survey data using Geographic Information Systems (GIS) software. The following will briefly outline the discipline of archaeological surveying and will demonstrate what equipment we use and the principles behind the utilisation of our equipment.

Archaeological Land Surveying
The constant need to accurately record the standing archaeological resource has been part of the discipline of archaeology since the earliest hand drawn maps and plans were created. The very earliest recording of an archaeological monument in Britain can perhaps be traced back to John Aubrey’s 1663 plan of Avebury, Wiltshire. Surveying monuments and landscapes was an important part of early archaeology. The Royal Commissions (on Ancient) and Historical Monuments professionalized the discipline of earthwork surveying in 1908. In 1922 OGS Crawford created a division within the Ordnance Survey to deal with the accurate depiction of antiquities on OS maps.

Traditional earthwork and field surveying techniques suffered from the rescue archaeology excavation boom of the 1960s and 1970s when traditional field survey skills became largely confined to specialists working with the Ordnance Survey or the various Royal Commissions . It is only recently, due in no small part to the recent theoretical approaches to landscape within archaeology, that earthwork and field survey techniques have again become desirable.

It is a fact that the accurate recording of the archaeological resource has still not been carried out on most of our scheduled monuments. It should be an intrinsic part of monument and landscape management as it allows a baseline to be set that can be measured against in the future. This will accurately allow a monitoring of damage and erosion that is occurring to the monument or landscape. This is especially relevant in the present climate of an increased recreational use of land for all activities ranging from walking, horse riding and mountain biking to the often illicit use of monuments as venues for motorised off-road activities such as quad biking, motocross bikes and 4x4 driving.

Land surveys, as well as providing a tool for heritage management, can answer research questions. Accurate earthwork and landscape survey requires a detailed coverage of the landscape on foot by the surveyor; new earthworks will often be found when performing a landscape survey. The detection of new earthworks in the landscape requires an archaeological understanding of the type and form of earthworks from all periods. These can be very ephemeral on the ground but the good surveyor will notice subtle differences in ground height and shape as distinct from the natural topography of the survey area. A recent survey of Chanctonbury Hill, Sussex, has perhaps revealed a hitherto unknown concentration of Middle Bronze Age Barrows that will change our current perception of how the landscape was perceived here prior to the construction of the Late Bronze Age hill fort (Chanctonbury Ring). It is in this way that topographical survey can be allied with theoretical approaches to landscape. Earthwork survey combined with geophysical survey and field walking will provide a holistic approach to the landscape and will provide a framework on which to target excavation. The Noviodunum Archaeological Project, Romania, uses such an approach to great effect and after four seasons of earthwork survey, field walking and geophysical survey the project has now begun to target areas for excavation as well as continuing the field survey strategy.

Modern archaeological land surveys are undertaken using a Total Station and/or Differential Global Positioning System (DGPS). These methods are both able to collect a mass of data very quickly and the systems that Archaeology South East uses can be operated by a single person. There may on occasion be the need to use a plane table. However as long as the surveyor is proficient then there is no true need to resort to plane table surveying and digital collection is likely to be more accurate and is of course three dimensional. Hachure plans can easily be created from digital data. Hachure plans are the standard and traditional way of displaying archaeological landscape data. The use of detail contour maps derived from surveys can impart more information than a simple hachure plan. The use of both forms of plan is desirable when publishing survey fieldwork.

Archaeological Surveying and Excavation
All archaeologists possess some surveying knowledge. When planning and recording archaeological sites by hand the archaeologist is utilising basic surveying principles. Plans will often use offsets from a known baseline (e.g. the site grid). Hand drawing plans can, however, lead to inconsistencies and inaccuracies. These errors will be minimised with an experienced planner. Even with experience hand drawn plans are time consuming to produce and they must also be digitized (a type of tracing with a digital device that replicates the hand drawing into a CAD package) before publication. Levels will often be taken on site by using a ‘dumpy level’. Essentially a level is taken in relation to a horizontal plane that in turn possesses a known level. In Britain this known level will normally be derived from the Ordnance Datum, or mean sea level, that is derived from a nearby bench mark. The bench mark is usually a physical mark in the wall of a building and has a known level in relation to the mean sea level. Dumpy levels can be surprisingly accurate even after long traverses but they are time consuming and require two people, one staff person and one taking the levels with the machine.

In relatively recent times both of the above methods of surveying have largely been replaced by using a total station or DGPS, particularly for large excavations and evaluations. The total station and DGPS allow a rapid collection of planning data that is collected in digital format and requires very little post processing. Another advantage of total station/DGPS planning is that levels are also ascribed to features as each point possesses its own Z co-ordinates as well as its X and Y co-ordinates. A total station must, of course, have a level obtained from an Ordnance Survey benchmark but DGPS surveying systems will provide a level from satellite information.

Total stations/DGPS are often also used to set out grids for geophysical survey and to set out evaluation trenches and excavation areas for excavation by machine. Co-ordinates are uploaded into the total station or DGPS system. These co-ordinates are normally tied in to the Ordnance Survey Grid for evaluation trenches and excavation areas but geophysical survey grids normally possess their own discrete set of co-ordinates for absolute accuracy (when setting out with total stations). DGPS can also be used to set out grids using NGR co-ords but the original data must be post-processed to set out accurate co-ordinates.

Case study: Hastings Castle, East Sussex

Contact: Mark Tibble