Filed under: Commentary, Guest Blogger, News, On Location, Technology | Tags: ancient footprints, photogrammetry, Preservation
Sarah Duffy, PhD is a Postdoctoral Research Associate at the University of York in the Department of Archaeology. In May of 2013, after a series of storms, ancient footprints were revealed on a beach near Happisburgh (pronounced “Hays-boro”) on Britain’s east coast in Norfolk (see a 6-minute video). The footprints were fragile and washing away a little day by day. Sarah was called to the site by Dr. Nick Ashton, Curator of Palaeolithic and Mesolithic collections at the British Museum, to document it. Here is our interview with Sarah about this dramatic discovery.
CHI: Sarah, can you tell us how you got involved in the project and what you found when you arrived?
Sarah: It really came down to good timing and an opportune meeting of research colleagues. When the footprints were discovered, I had just begun working with Dr. Beccy Scott at the British Museum on a project based in Jersey called “Ice Age Island”. Beccy and my partner, Dr. Ed Blinkhorn, another early prehistoric archaeologist, have collaborated for many years, and he introduced us. During the week of the discovery, Beccy happened to be at a research meeting with Dr. Nick Ashton and suggested that he get in touch with me about the Happisburgh finding.
The next day, I received a call from Nick who asked if I would be able to take a trip to Norfolk to record some intertidal Pleistocene deposits at Happisburgh. Having just completed my PhD thesis (a “dissertation” in US currency), I was up for an adventure and ready to take on the challenge, and so I was on a train to the southeast coast two days later.
My first plan of action was to figure out how on earth you pronounced the name of the site! The next step was to figure out what equipment I would need to have available when I arrived. This proved somewhat challenging, as I had never visited the Norfolk coast, and it seems quite humorous in hindsight that one of the pieces of kit I requested was a ladder.
All of this said, the urgency to get the site photographed became clear when I showed up one very rainy afternoon in March. Standing on the shore, I felt very privileged to have been invited to record such an important set of features, which disappeared within only weeks of their discovery by Dr. Martin Bates.
CHI: What were your goals in the project and why did you choose to shoot images for photogrammetry? Can you tell us a little bit about your approach?
Sarah: Since I wasn’t sure what to expect when I reached the site, I took both photogrammetric and RTI kit materials with me. I intended to capture the 3D geometry of the prints with photogrammetry and subtle surface relief with RTI. However, when I arrived, both the weather and tidal restrictions limited the time we were able dedicate to recording. I therefore focused my efforts on photogrammetry, which proved a flexible and robust enough technique that we were able to get the kit down the cliff side in extremely challenging conditions and capture images that were used later to generate 3D models.
Based on the looming return of the tide and the amount of time required to prepare the site, our window of access was quite small. While I took the images, aided by Craig Williams and an umbrella, the rest of the team battled the rain and tide by carefully sponging water from the base of the features. As mentioned, I originally intended to capture images from above the site using a ladder. However, as the ladder immediately sank into the wet sand, I was forced to find other means of overhead capture: namely Live View, an outstretched arm, and umbrella. There was just enough time to photograph the prints, loosely divided into two sections, using this recording approach before we had to retreat back up to the top of the cliff (and to a very warm pub for a much deserved fireside pint!).
CHI: When you got back to your office, how long did it take you to process the images, and what software did you use?
Sarah: Originally, I used the Standard Edition of PhotoScan by Agisoft, later returning to the image set in order to reprocess it with their Professional Edition. PhotoScan’s processing workflow is relatively straightforward, and the time required to generate geometry is somewhat dependent on the hardware one has access to. The post-processing of the images was by far the most time-consuming component of the processing sequence. Since the software looks for patterns of features, there was a substantial amount of image preparation that needed to be completed first, before models could be produced. For example, rain droplets on the laminated surface that contained the prints needed to be masked out, as well as the contemporary boot prints that accumulated in the sand that surrounded the site throughout the image sequence.
CHI: How were the 3D models you produced used by the other archaeologists involved with the site?
Sarah: Once the models had been generated, the rest of the team, including Nick Ashton, Simon Lewis, Isabelle De Groote, Martin Bates, Richard Bates, Peter Hoare, Mark Lewis, Simon Parfitt, Sylvia Peglar, Craig Williams, and Chris Stringer, wrote the paper on the results. Nick Ashton and Isabelle De Groote closely analyzed the models of the prints in order to study size, movement, direction, and possible age of the early humans who might have created these features. Isabelle later worked with the 3D printing department at Liverpool John Moores University in order to have one of the digital models printed.
CHI: Since the footprints were washed away, your images are the best record of the site that exists. Are the 3D models accessible? What will you do to preserve this material?
Sarah: Coverage of the footprints, including excerpts of the digital models that I generated and the 3D printout, can be viewed at the Natural History Museum exhibit in London, Britain: One Million Years of the Human Story, which closes September 28th. Findings from the analysis have also been published in PLOS ONE, an open-access, peer-reviewed scientific journal.
As mentioned, when I visited the site last March, I had hoped to undertake a RTI survey. Although conditions on the day of recording did not permit multi-light capture, I have since been able to generate virtual RTI models that reveal the subtle topography of the prints. An excerpt of one of these models can be viewed on my website.
Additionally, the research team, in collaboration with the Institute of Ageing and Chronic Disease at Liverpool, are currently working on extracting further information from the image set. Findings from this work will be made available in the future. Once analysis is complete, the images and resulting models will be archived with the British Museum.
CHI: Thank you for your time, Sarah, and what a great story!
Sarah Duffy has been collaborating with Cultural Heritage Imaging (CHI), including taking CHI’s training in Reflectance Transformation Imaging (RTI) and working with the technique since 2007 while she was a graduate student in Historic Preservation at the University of Texas at Austin. Sarah authored a set of guidelines for English Heritage on RTI. During her doctoral work, she also began to apply her imaging skills in the area of photogrammetry.