Periodic Reporting for period 4 - CALI (The Cambodian Archaeological Lidar Initiative: Exploring Resilience in the Engineered Landscapes of Early SE Asia)
Reporting period: 2019-09-01 to 2020-02-29
The Cambodian Archaeological Lidar Initiative is an ambitious research program involving researchers from several countries seeking to advance airborne laser scanning, or lidar, as a method for investigating human-environment interactions over the long-term, from prehistory until the present day. The surface of the Earth records traces of past human activity in the form of subtle topographic variation, which can be mapped and decoded to understand the growth and decline of early societies, their cities, and their networks of communication and interaction. In many areas of the world, however, and in particular in tropical regions, vegetation has tended to obscure the remnant traces of the past. In Southeast Asia for example, the great temple complexes of the Khmer such as Angkor are famous for their monumental remains, but remain very poorly understood as places that people actually lived, and tropical forest environments everywhere retain a reputation as marginal, wild, and inhospitable terrain for the development of complex societies. Lidar technology offers a new perspective on the past thanks to its unique ability to ‘see through’ the vegetation that obscures these places. Our objective is to complete the most extensive archaeological lidar survey ever achieved, with a view to revealing the full complexity of early urbanism in the tropical forests of Southeast Asia. In particular, we are interested in understanding the adaptive strategies that early societies used to survive the harsh monsoon environment, and whether or not those strategies fostered resilience, or perhaps created systemic vulnerabilities, in the face of long-term environmental change. In looking at questions of urban extensification, infrastructural inertia, environmental degradation and social and environmental change, the CALI project addresses themes and issues that resonate strongly into the contemporary world.
The CALI project has completed all lidar data acquisition, and have amassed a huge archive of digital geospatial data covering more than two thousand square kilometres of the Cambodian landscape, including several billion points from the lidar sensor and many thousands of conventional aerial photographs. We established a dedicated lidar laboratory at the research base of the French Institute of Asian Studies (EFEO) in Siem Reap, where analysts have been working to systematically identify and map features within the lidar data, through visual inspection and manual digitisation. We now have comprehensive maps of every major archaeological landscape in Cambodia, spanning several thousand years from the Bronze Age, through the Angkor Period and the collapse of the Khmer Empire, right up to the present day. It is a unique and extraordinary archive of human behaviour which records the dynamic interplay between humans and their environment over vast scales of time and space, and provides a kind of laboratory for evaluating different hypotheses about the past. In some areas, such as Angkor, we have added new detail to a body of knowledge that has been building for a century and a half; in other areas, entire engineered landscapes have emerged from beneath the forest cover. We have completed the ground verification component of our work, which involves systematically validating our interpretations of the lidar data on the ground, and have revised archaeological maps accordingly. The final stage of the project has concluded with an emphasis on publication and dissemination of the data and the research results in peer reviewed academic contexts.
Key outcomes from the CALI project have already been published at this stage in a series of peer-reviewed papers. We have outlined the most significant findings from the analyses of the lidar data, for example the identification of urban and agricultural networks around several of the major temple complexes of the Khmer Empire. This work demonstrates that lidar is an extremely effective tool for identifying archaeological remains in the tropical forest environment of Southeast Asia, even in areas that have been intensively studied for many years. In fact, it now becomes clear from the CALI project, and from a handful of similar projects elsewhere the world, that we have substantially underestimated the extent to which past societies managed, transformed and impacted supposedly ‘pristine’ tropical forest environments. On a more granular level, we have worked with engineers and other scientists to realise the full analytical potential of lidar data, not just for site discovery and mapping but to create sophisticated models of how water infrastructure functioned and failed, and how environmental factors such as rainfall, flow, deforestation and erosion left identifiable patterns in the landscape which record societal challenges and adaptive strategies. We have also completed a broad comparative survey across all of the sites in our archive, in order to assess the relevance of what we learn to problems we face in the contemporary world. Beyond this analytical work, the CALI project has focused on technical solutions to dealing with massive datasets, and has collaborating with various other teams to develop automated feature-recognition algorithms; to deploy web-based tools for data sharing, integration, and collaboration; and to define protocols for eventual open access to the archive.