By Nicole Lathrop
You can’t see the forest through the trees. Likewise, it’s hard to see the feature when you’re standing on it.
Drones have created opportunities to see the invisible, record the inaccessible and conceptualize the intangible. When combining drone technology with newer computer processing options, the sky, or – in an archaeologist’s case – beneath the dirt, is the limit.
New technology like Lidar makes it possible to quickly and accurately map topographical features through the use of light pulses that, when reflected back to the camera, can create 3D information. The pulsing of light also allows the detection of surface through a forest or under bodies of water[i]. The downside of Lidar, however, is that it is often cost prohibitive.
As with most technological advancements, where there’s a will, there’s a way. For 3D modeling other methods have since been created to complete similar tasks for a fraction of the costs. Programs like WebODM (Web Open Drone Model) provide free platforms for image compilation that result in a rendered 3D topographical output. Pix4D capture provides an app that allows for drone control for an automated image compilation process, resulting in 3D rendering in-app. Unfortunately, Pix4D only works with select drones, while WebODM is computer based and only required the input of the many photographs to create such a model.
When taking the hundreds of photographs for a thorough 3D model, I have found that the use of my bright orange landing pad makes for a great reference in images, and will often take a GPS point, which can then latter be used as a marking point in ArcGIS or QGIS to put our rendering in a map context.
Now that we have talked a bit about the ‘How?’, lets talk more about the ‘Why?’.
Areal archaeology has become the frontier of archaeological discovery. Originating with the use of areal photography and satellite imagery, archaeologists have been able to use this method to distinguish abnormalities in the topological landscape for potential sites[ii]. This method allows a new perspective in the observation of sites, and because squares, circles and shapes interconnected are not normally a naturally occurring[iii], It makes it easier to deduce where a site is.
This foresight into exact locations for archaeological sites reduces a lot of the ‘guess work’ for the initial excavation and study of the site. Combined with knowledge of local water sources, soil farming suitability and other habitation factors, we can learn a lot about a site now before even breaking ground for excavation.
Multi-spectral imaging, often used in agriculture to determine the health of crops, can also be applied to these archaeological concepts. One such indicator of a below surface feature under crops is the resulting stunted growth of the crops due to the inability for the roots to extend further. While this results in a 3 dimensional ‘tell’ of the crops being shorter. Similar results can occur with soil types resulting in an altered spectral growth of the crop[iv]. This means that visibly the plants are identical, though using multi-spectral imaging can see the minute differences in the light absorption of the plants.
With the rapid advancement of this technology, and our accessibility to use it in an archaeological setting, it is appropriate to conclude that the field of Drone Archaeology is still in its infancy.
[i] Moller, A. and Fernandez-Diaz J. 2019 Airborne Lidar for Archaeology in Central and South America https://lidarmag.com/2019/04/01/airborne-lidar-for-archaeology-in-central-and-south-america/
[ii] Oltean, I. 2016 Recovering Lost Landscapes https://a-a-r-g.eu/wp-content/uploads/2019/02/AARGnews53-1.pdf
[iii] Pettit, H. 2016 Aerial pictures reveal Englands Archaeological Sites https://www.newscientist.com/article/2099195-aerial-pictures-reveal-englands-ancient-archaeological-sites/
[iv] Lasaponara, R. and Masini, N. 2007 Detection of Archaeological crop marks by using satalite QuickBird Multispectral Imaging https://doi.org/10.1016/j.jas.2006.04.014
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