Weipa, Take Three (by Casey Beresford)

Well here we are again in Weipa for another field season! I have to say it’s really great to be back again and I’m enjoying the climate (i.e. warmer than the 10°C or so in Auckland where I’m from!), and the company of everyone involved in the WARPPED project who have travelled from all corners of the globe to be here.

The results from the last couple of year’s fieldwork in Wathayn, on the Embley River have been very interesting. The radiocarbon dates taken from the shell deposits excavated in 2010 and 2011 demonstrate some interesting patterns resulting from different taphonomic and post-depositional processes operating at different times and in different parts of the landscape in Wathayn. Untangling how humans and the environment worked together to produce what we see today (and are able to excavate) continues to be a key focus of our research framework and guides our excavation methods. With this in mind we have generated some new approaches to our survey methods to make comparing shell deposits easier, faster and importantly, more consistent.

How do we collect geographic information for features and items within the landscape at Wathayn?

The robotic total station which we use for collecting our survey data has no capability within itself to “know” its geographic position in the world. Instead it creates an arbitrary landscape between two “known” points which are entered manually (e.g. GPS coordinates) to calculate an unknown. Essentially the total station uses trigonometry to measure the distance and angle between the two “known” points to calculate the location of an “unknown” target. A target might be a pole with a prism attached to the top that a person can move around. By levelling the pole and correcting for the height of the prism from the ground, we can use the total station to calculate a geographic position within the landscape. The total station is very accurate and precise at calculating the unknown position, however, it is crucial that the “known” GPS coordinates are also both accurate and precise, with a low margin of error. This year the coordinates for the geographic control points used by the total station are gathered using a GNSS system. GNSS uses satellites from America and Russia to triangulate geographic locations on Earth. In Wathayn, we have set up a localised base station to collect real-time differentially corrected coordinates so that we are able to know our true geographic position when collecting data in the field. This is crucial as excavation naturally involves removing objects from one context to another (e.g. digging sediment and moving it using buckets to a spoil heap), however, the initial placement of these objects (whether it be charcoal, an artefact or shellfish remains) is essential for understanding how a combination of human and natural processes may have interacted to create the landscape features which are visible today. Once an object is removed from its context, much of its information potential in terms of understanding human-environment interaction is lost. Therefore, we need a highly accurate and precise method for collecting the spatial information associated with different items in the landscape as this contextual information can only be collected once.

Using the robotic total station to “draw” stratigraphic sections

Archaeological information is not often recorded in a consistent manner, making interregional analysis between different institutions and projects difficult (sometimes impossible!). Last year we used traditional methods for recording the internal structure of the shell deposits, using graph paper and pencils to record the different layers and features present in the section of the trench walls. Drawing the sections by hand is time consuming and difficult using a line levels and measuring tapes. As you can imagine, there can be a lot of variation in how the different layers of shell and features within each deposit are represented by different individuals. Representation of a particular stratigraphic layer may vary depending on an individual’s level of experience or their learned academic discipline, not to mention whether their handwriting is legible or not! The stratigraphic information was later digitised in the lab once we left the field. This year we are trying something new, using a robotic total station to “draw” the stratigraphy. After excavation and cleaning down of the exposed sections, the survey team (after some discussion), places coloured nails along layer boundaries and around features in the trench wall. The total station is then used to measure the coordinates of each nail. Each point is assigned a number of characteristics (or attributes), which define the layer above. These attributes are tabulated and stored within the total station alongside their associated geospatial information. For example, some of the attributes for defining a layer include: soil colour, texture, fabric, boundary form and description, as well as proportion of shell relative to sediment and degree of fragmentation. At the end of each work day, this data is transferred to a computer and converted to a shapefile which can be inserted into a 3D landscape and the points converted to line features. The stratigraphy then becomes a 3D object which can be rendered and georeferenced with colour and/or texture information collected using photographs and charts. This approach has many benefits. Some examples include: no need to use a line or spirit level in the field, more than one stratigraphic section is able to be viewed at the same time and at any angle, descriptions are associated with the drawing, and 3D drawings are able to be saved, accessed and viewed by many people at once, simply by copying and distributing the map files. This is the first time that we have attempted to use this method and the results are looking very promising!