Terrestrial Metric Survey

Terrestrial Metric Survey is arguably one of the most traditional non-invasive survey techniques still actively used by professionals today. Advancement in technology has made collecting data a much faster and more accurate and precise exercise.

Survey equipment that will be deployed by the CHERISH team include both Total Station Theodolites (TST) and Global Navigation Satellite System (GNSS) base stations and rovers. This equipment will be used to gather metrically accurate 3D data for a range of different purposes. This includes the location of sites and monuments within the national grid coordinate systems of Ireland and Great Britain, the establishment of control networks for monitoring purposes and the geo-referencing of data derived from other sources such as terrestrial laser scanning or UAV photography.

Total Station or Total Station Theodolite (TST) that measures angles and distances from and to a specified point within a direct line of site. Total stations are particularly useful in the survey of buildings where reflectorless functionality enables the measurement of a point without the need to place a prism, as well as in areas where obstruction of the sky and thus satellite signals makes GNSS survey difficult such as woodland or around tall buildings.

Total station survey on Skellig Michael, IrelandTotal station survey on Skellig Michael, Ireland

Global Navigation Satellite Systems (GNSS); or Global Positioning Systems (GPS) as it is sometimes known use satellites in orbit above the earth to provide positional, navigational and tracking services anywhere in the world. A variety of GNSS systems are available which offer differing degrees of accuracy from navigation-grade GNSS receivers (metre accuracy), mapping-grade GNSS receivers (0.5-5m accuracy) and survey-grade GNSS receivers (centimetre level accuracy).

These systems will be used to undertake detailed analytical survey to provide an understanding of sites, monuments and landscapes. Survey with TST and GNSS require the surveyor to use their judgement, experience, knowledge and interpretative skill to decide what will be recorded. In the case of earthworks this could be deciding which features are man-made as opposed to natural and where the top, bottom or breaks of slope lie. When concerning standing remains the surveyor is required to identify subtle changes in alignment or modification to the fabric of a structure, for example through the insertion or blocking of a window.

GNSS terrestrial survey at Grassholm, WalesGNSS terrestrial survey at Grassholm, Wales

Analytical survey assists in the interpretation of a site, monument or landscape showcasing history, development, form and condition, and highlighting chronological relationships. The principal ways of presenting this is through scaled interpretative drawings commonly produced using graphics packages such as AutoCAD. For a building this might comprise a series of phased plans and elevations, whilst for an earthwork this is through a hachure plan. Using hachures as opposed to contours for earthworks has many advantages; they clearly distinguish between natural and artificial slopes, give a consistent depiction of features and show chronological relationships between them.

Example of terrestrial survey plan, Grennalla Point FortExample of terrestrial survey plan, Grennalla Point Fort, Wales