Topographical survey at Portus

Hi, my name is Stephen Kay and I’m responsible for the topographical survey on the Portus Project. I am currently the Molly Cotton Fellow at the British School at Rome (www.bsr.ac.uk), one of the partner institutions for the field school. My research interests are focused on landscape archaeology, in particular on Roman urbanism in central Italy. Away from the Portus Project my work at the British School at Rome involves geophysical survey and working on the Segni Project, a 3 year research project looking at the changing urbanistic plan of the ancient Latin town of Signia, using techniques such as geophysics, laser scanning, topographical survey and excavation. The project is jointly run by the Museo Archeologico Comunale di Segni (www.museosegni.it) and the BSR (http://www.bsr.ac.uk/research/archaeology/ongoing-projects/segni-project).

I have been involved with the research at Portus since it began in 1997 with the first geophysical (magnetometry) survey. Over the course of the following 8 years an area of c.178ha was surveyed, which was subsequently published in Portus. An Archaeological Survey of the Port of Imperial Rome (2005).

My current work at Portus involves topographical surveying and aerial photographs through the use of UAV’s, more commonly known as drones. In order to fully understand the complex stratigraphy and standing walls, the project draws upon techniques such as topographical and building survey (using Total Stations and Global Positioning Systems), photogrammetry, laser scanning and Reflectance Transformation Imaging (RTI). The combination of these technologies allows us to examine, record and present the surface layers of the site and its artifacts in extraordinary detail.

Topographical survey provides the framework for all the work undertaken on site, ensuring the data is accurately and precisely located within the same coordinate system. Over the course of the preceding geophysical survey, a local coordinate control network was established for the work at Portus, which was subsequently globally located using a GPS from 5 fixed control points around the site. The survey is also tied into features shown on digital maps of the survey area. These features act as further control stations and enable cross-checking using triangulation and are further strengthened by the surveying of a closed loop traverse. https://twitter.com/stephenjohnkay/status/450971545801089024

In practice on site this means that all standing structures, collapsed masonry, stratigraphical layers, levels, small finds and environmental samples discovered by the excavation are recorded using a Total Station. A Total Station (the Portus Project uses a Leica TCR307 and TS02) is an electronic theodolite integrated with an electronic distance meter (EDM) to read distances from the instrument to a particular point. Coordinates of an unknown point relative to a known coordinate can be determined using the Total Station as long as a direct line of sight can be established between the two points. Angles and distances are measured from the total station to points under survey, and the coordinates (easting, northing and elevation) of surveyed points relative to the total station position are calculated using trigonometry and triangulation.

During the course I will be discussing all aspects of the topographical work and how we fit all the pieces of the jigsaw together, in order to produce the excavation plans and elevations. In particular I will be doing general day-to-day recording supporting the excavation whilst also using other techniques such as photogrammetry https://twitter.com/stephenjohnkay/status/464711536398049281 This data then forms the basis for other work, such as the 3D modelling, in order that all data is accurately positioned and sized.