Charles Higham: Drones and DNA

6 mins read

When I was a student of archaeology, I kept a small notebook of quotes from eminent scholars that might prove useful at exam time. One in particular sticks in the memory from those hot summer days when the countdown to the first set of questions accelerated. It came, I recall, from O G S Crawford in an early edition of Antiquity. He said something along the lines of: ‘to be a successful archaeologist, you have to be like a bird to fly over the landscape’. Those where the days when Dr St Joseph, known as ‘Holy Joe’, was filling the map of Roman Britain with forts, roads, and towns through his aerial photographs.

Now new developments in this field, which will soon be routine, are changing the way we archaeologists work.

A miniature LiDAR machine carried across the excavation square at Non Ban Jak produced a detailed contour map of the surface in minutes.

Time fliers

Much attention has recently been given to the stunning impact of the LiDAR surveys at Angkor (see our cover story, CWA 77). Virtually at a stroke, issues that have been contentious or opaque for decades have been resolved and, in the words of Roland Fletcher, ‘spawned generations of PhDs’. I have visited Angkor Wat many times, and wondered what lay in the extensive area that lies between the central temple and the surrounding moat. An hour or two and millions, probably billions, of measurements with the laser that penetrates the forest and bounces back the precise layout of the land below has now mapped a grid of streets, house mounds, and ponds that are evidence of a tightly planned urban complex. A mile or two to the north of Angkor Wat, lies the walled city of Angkor Thom. Apart from the central temples and palace, it is covered with a dense forest. Again, a morning’s overflight has generated the urban plan, with its streets, canals, houses, and ponds. Moreover, the grid pattern – as precise as that of New York City – extends beyond the moats into the surrounding area. Up on the Kulen Hills, the foundations of the first city of Angkor, known only through inscriptions, has emerged from forested oblivion.

Nor is LiDAR confined to Angkor. In Shanghai last December, I met Richard Hanson who gave me a sneak preview of the results of his own LiDAR survey at the massive early Maya centre of El Mirador. At Carakol, also in the Maya lowlands, the field systems, temples, and residences have been mapped in minutes in a forested landscape where ground surveys would take years, and probably be less accurate.

Even the availability of straightforward aerial photographs has been magnified with easy and free access to Google Earth. For his postgraduate dissertation at the Australian National University, Glen Scott has pored over the entirety of the Khorat Plateau in Northeast Thailand, produced a definitive distribution map of the Iron Age moated settlements, then computed their area and the number of moats, before interpreting their distribution relative to rainfall and elevation.

Charles Higham and graduate student Helen Heath examine the drone.

I have been exploring some of these moated sites for years, and have traced, again from Google Earth, intriguing straight lines emerging from the moats of some of them, that run for hundreds of metres across the flat landscape, and sometimes turn right angles to proceed further on. So I was particularly interested in the results of detailed remote-sensing of the Iron Age sites in the Angkor region by Scott Hawken. He has mapped a myriad of rice fields that stretch over at least four periods. The latest are the large, square field plots laid out under the dreaded Khmer Rouge regime of the 1970s. These override the dense set of Angkorian fields that we now know were irrigated from the huge reservoirs that are such a prominent part of the modern landscape. Prior to these, there are the fields of the early Historic Chenla period (AD 550-800), but what I found crucial to any interpretation of the late prehistoric period was the possible presence of permanent fields round the Iron Age settlements there. This reflects a model that has been generated from our fieldwork in the Upper Mun Valley of the Khorat Plateau, only 250km to the north. Fixed fields, possibly irrigated from the broad moat/reservoirs, would date to the period when we find heavy iron ploughshares and sickles placed with the dead. Ploughing in irrigated fields is a key to identifying and tracing the rise of social inequality, a phenomenon recognised as a feature of all early states, and seen with particular clarity at Angkor.

The future of fieldwork?

With a buzzing engine, we have lift off! The drone is about to start mapping.
With a buzzing engine, we have lift off! The drone is about to start mapping.

This brings me to my recently completed fifth season of excavations at the moated Iron Age settlement of Non Ban Jak. Two years ago, by a fortunate opportunity, I met M R Saksiri Kridakorn, the chief executive of MapPoint Asia in Bangkok. He expressed an interest in visiting our excavations and, with family and colleagues, he spent a day with us. I took them to several of our sites and
explained my interest in detailed mapping not just of the mounded sites themselves, but of the surrounding landscape. I met him again a year ago when I gave a lecture in Bangkok, and we firmed up plans for deploying all the techniques in his toolkit on site. So, in January this year, we met in Bangkok to formulate our plans. We pored over detailed aerial photos of our moated sites, and discussed the potential of drone overflights. Four weeks later, he and his team drove up to Non Ban Jak, and got to work.

I had, of course, heard of drones, but mainly from news bulletins describing them killing insurgents somewhere. So my first close-up examination of one revealed what a masterpiece of miniaturisation and technical sophistication they are. There are propellers powered by a battery, and the tiny camera angled to the ground sends instant signals down to the monitor screen below.
We mapped out the flight path to cover the site and its surrounds, and up the drone buzzed. It systematically criss-crossed the site according to its instructions, and we could follow what it was seeing. Simultaneously, it was recording countless measurements that would be processed and employed to produce our detailed maps.

This was but one of the survey techniques that came up from Bangkok. There was also a fixed-wing creation. Again programmed with a flight path to cover three other moated sites in our study area, I did not even need to see it. The team found a good flat area nearby for it to take off and land, and, once airborne, it was off and away to cover and map each of its targets. When we are actually digging, we open an area of 10m by 10m and measure each feature identified as we go down, mapping with pencil and graph paper and recording the depth below our datum for key referents, like the artefacts associated with a burial, or the depth of a pit. Saksiri had also brought a hand-held LiDAR unit, and asked us to clear the excavation square of people and tools. An operative then went down into the square and walked over it holding the unit. Within a matter of minutes, we were looking at a detailed plan of the surface on a computer screen. Is this the future for archaeological recording?

Harnessing DNA

I have seen enough of the raw results on site to know that when the detailed plans are finalised in Bangkok, I will be much better informed than ever before, and all thanks to techniques one could only have fantasised over a few years ago.

Returning to my student days, I remember the issue of migration in prehistory being a prominent issue of the day. To what extent, we pondered, was cultural change the result of internal stimulus or the impact of new people moving in? This remains an important issue, but now we have methods with the potential to replace debate by an assurance that migration did take place. One of these employs the isotopes in bones and teeth that are determined by where an individual was raised. Another, of course, is the analysis of ancient DNA. The latter has recently revealed the large-scale migrations that occurred in Central Asia and Europe during the Bronze Age.

How I envy those working where the cold means that aDNA can be extracted from human remains. I have tried since 1992 to cooperate with specialists to do the same in Southeast Asia. I would love to know more about the population history of the communities I have illuminated through my excavations. There have been some rare breakthroughs. Ancient DNA from the people of Man Bac, a Neolithic site in northern Vietnam, is matched by that from Weidun in the lower Yangtze, revealing strong evidence for the expansion southward of early rice farmers. The DNA from rice itself has confirmed this. But for my sites, virtually a total blank. Recent advances in the extraction of DNA from bone have now encouraged further attempts. Eske Willerslev of the Universities
of Copenhagen and Cambridge is keen to replicate in Southeast Asia his seminal results from Central Asia. Samples are en route to his laboratory as I write. This, like the drones, is a further instance of the rapid changes that are such an exciting part of modern archaeological enquiry.

This article appeared in CWA 78. Click here to subscribe.

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