Damian Evans

A comprehensive archaeological map of the world's largest preindustrial settlement complex at Angkor, Cambodia

The great medieval settlement of Angkor in Cambodia [9th–16th centuries Common Era (CE)] has for many years been understood as a “hydraulic city,” an urban complex defined, sustained, and ultimately overwhelmed by a complex water management network. Since the 1980s that view has been disputed, but the debate has remained unresolved because of insufficient data on the landscape beyond the great temples: the broader context of the monumental remains was only partially understood and had not been adequately mapped. Since the 1990s, French, Australian, and Cambodian teams have sought to address this empirical deficit through archaeological mapping projects by using traditional methods such as ground survey in conjunction with advanced radar remote-sensing applications in partnership with the National Aeronautics and Space Administration (NASA)/Jet Propulsion Laboratory (JPL). Here we present a major outcome of that research: a comprehensive archaeological map of greater Angkor, covering nearly 3,000 km2, prepared by the Greater Angkor Project (GAP). The map reveals a vast, low-density settlement landscape integrated by an elaborate water management network covering >1,000 km2, the most extensive urban complex of the preindustrial world. It is now clear that anthropogenic changes to the landscape were both extensive and substantial enough to have created grave challenges to the long-term viability of the settlement.

Uncovering archaeological landscapes at Angkor using lidar

Previous archaeological mapping work on the successive medieval capitals of the Khmer Empire located at Angkor, in northwest Cambodia (∼9th to 15th centuries in the Common Era, C.E.), has identified it as the largest settlement complex of the preindustrial world, and yet crucial areas have remained unmapped, in particular the ceremonial centers and their surroundings, where dense forest obscures the traces of the civilization that typically remain in evidence in surface topography. Here we describe the use of airborne laser scanning (lidar) technology to create high-precision digital elevation models of the ground surface beneath the vegetation cover. We identify an entire, previously undocumented, formally planned urban landscape into which the major temples such as Angkor Wat were integrated. Beyond these newly identified urban landscapes, the lidar data reveal anthropogenic changes to the landscape on a vast scale and lend further weight to an emerging consensus that infrastructural complexity, unsustainable modes of subsistence, and climate variation were crucial factors in the decline of the classical Khmer civilization.

The water management network of Angkor, Cambodia

Meticulous survey of the banks, channels and reservoirs at Angkor shows them to have been part of a large scale water management network instigated in the ninth century AD. Water collected from the hills was stored and could have been distributed for a wide variety of purposes including flood control, agriculture and ritual while a system of overflows and bypasses carried surplus water away to the lake, the Tonle Sap, to the south. The network had a history of numerous additions and modifications. Earlier channels both distributed and disposed of water. From the twelfth century onwards the large new channels primarily disposed of water to the lake. The authors here present and document the latest definitive map of the water network of Angkor.

Mapping Above-Ground Biomass in a Tropical Forest in Cambodia Using Canopy Textures Derived from Google Earth

This study develops a modelling framework for utilizing very high-resolution (VHR) aerial imagery for monitoring stocks of above-ground biomass (AGB) in a tropical forest in Southeast Asia. Three different texture-based methods (grey level co-occurrence metric (GLCM), Gabor wavelets and Fourier-based textural ordination (FOTO)) were used in conjunction with two different machine learning (ML)-based regression techniques (support vector regression (SVR) and random forest (RF) regression). These methods were implemented on both 50-cm resolution Digital Globe data extracted from Google Earth™ (GE) and 8-cm commercially obtained VHR imagery. This study further examines the role of forest biophysical parameters, such as ground-measured canopy cover and vertical canopy height, in explaining AGB distribution. Three models were developed using: (i) horizontal canopy variables (i.e., canopy cover and texture variables) plus vertical canopy height; (ii) horizontal variables only; and (iii) texture variables only. AGB was variable across the site, ranging from 51.02 Mg/ha to 356.34 Mg/ha. GE-based AGB estimates were comparable to those derived from commercial aerial imagery. The findings demonstrate that novel use of this array of texture-based techniques with GE imagery can help promote the wider use of freely available imagery for low-cost, fine-resolution monitoring of forests parameters at the landscape scale.

Mapping and Characterizing Selected Canopy Tree Species at the Angkor World Heritage Site in Cambodia Using Aerial Data

At present, there is very limited information on the ecology, distribution, and structure of Cambodia’s tree species to warrant suitable conservation measures. The aim of this study was to assess various methods of analysis of aerial imagery for characterization of the forest mensuration variables (i.e., tree height and crown width) of selected tree species found in the forested region around the temples of Angkor Thom, Cambodia. Object-based image analysis (OBIA) was used (using multiresolution segmentation) to delineate individual tree crowns from very-high-resolution (VHR) aerial imagery and light detection and ranging (LiDAR) data. Crown width and tree height values that were extracted using multiresolution segmentation showed a high level of congruence with field-measured values of the trees (Spearman’s rho 0.782 and 0.589, respectively). Individual tree crowns that were delineated from aerial imagery using multiresolution segmentation had a high level of segmentation accuracy (69.22%), whereas tree crowns delineated using watershed segmentation underestimated the field-measured tree crown widths. Both spectral angle mapper (SAM) and maximum likelihood (ML) classifications were applied to the aerial imagery for mapping of selected tree species. The latter was found to be more suitable for tree species classification. Individual tree species were identified with high accuracy. Inclusion of textural information further improved species identification, albeit marginally. Our findings suggest that VHR aerial imagery, in conjunction with OBIA-based segmentation methods (such as multiresolution segmentation) and supervised classification techniques are useful for tree species mapping and for studies of the forest mensuration variables.

Residential patterning at Angkor Wat

Considerable attention has been devoted to the architecture and art history of Cambodias Angkor Wat temple in the last century. There has, however, been little research on the functions and internal organisation of the large rectangular enclosure surrounding the temple. Such enclosures have long been assumed to have been sacred precincts, or perhaps ‘temple-cities’: work exploring the archaeological patterning for habitation within them has been limited. The results of LiDAR survey and excavation have now revealed evidence for low-density residential occupation in these areas, possibly for those servicing the temple. Recent excavations within the enclosure challenge our traditional understanding of the social hierarchy of the Angkor Wat community and show that the temple precinct, bounded by moat and wall, may not have been exclusively the preserve of the wealthy or the priestly elite.

The landscape of Angkor Wat redefined

For over a century, the landscape of Angkor Wat and its surrounding area have been the focus of archaeological study. These studies have been constrained substantially, however, by a lack of chronological resolution in the features of the landscape and the difficulty of dating elements of the cultural assemblage. Recently obtained LiDAR data have transformed understanding of the Angkor Wat complex, enabling archaeologists to map terrain usually obscured by dense and protected vegetation. The results have informed targeted ground-based research, demonstrated previously unknown relationships between elements of the site, shown that the complex is much more extensive than previously thought and revealed a massive, unique and unknown structure.

Reimagining the City of Fire and Iron: A landscape archaeology of the Angkor-Period Industrial Complex of Preah Khan of Kompong Svay, Cambodia (ca. 9th to 13th centuries A.D.)

In the archaeological literature regional centers often receive far less attention than capital regions and the medieval Khmer Empire (ca. 9th to 15th centuries a.d.) is a classic case in point. At its height, the Khmer Empire stretched across much of mainland Southeast Asia, and it remains the most extensive dominion in the history of the region. To date, however, relatively little archaeological work has been completed outside of the capital of Angkor, and we have a limited understanding of the broader dynamics of the Empire. In this paper we begin to address this lacuna at the remote monumental complex of Preah Khan of Kompong Svay, the largest of all the Angkor-period regional centers. We describe the use of remote sensing and ground survey methods to produce the first comprehensive archaeological map of the site. The map data are used to evaluate conventional interpretations of the site as a major industrial complex, urban center and military outpost. The findings have implications for our understanding of early urbanism, industrial production and imperial expansion in the region.

Angkor Wat: an introduction

Abstract The temple of Angkor Wat, visited annually by tens of thousands of tourists, is without question one of the great archaeological sites of mainland Southeast Asia. Less obvious to the casual visitor is that it was but a single element in a large dispersed city. The papers in this special section demonstrate how recent research using LiDAR, ground-penetrating radar and targeted excavation have transformed our understanding of Angkor Wat and its surroundings.

Uncovering Angkor: Integrated Remote Sensing Applications in the Archaeology of Early Cambodia

For more than a decade the multinational (Australian, French, Cambodian) Greater Angkor Project has been investigating the rise and fall of medieval urbanism at Angkor, in Cambodia, using a diverse range of techniques, including extensive use of remotely sensed imagery to find, map and analyse elements of urban form. The research activities have focussed on the role of Angkor’s elaborate water management system in the demise of the urban complex, and has recently been expanded to include nearby ‘secondary’ settlement complexes such as provincial centres and ephemeral capitals. In such a research agenda, it is crucial to gain a full understanding of the original hydrological layout of the Angkor basin, in order to provide essential insights into human modifications to the natural hydrology and topography. To this end, a number of multispectral satellite images (including QuickBird and ASTER) were processed and analysed to identify palaeo-environmental traces and anthropogenic features relevant to the identification of remnants of the original fluvial system. Vegetation indices (VI), Vegetation suppression and Principal Component Analysis (PCA) were adopted as the primary procedures in order to detect relevant traces over differing environments such as perennially forested zones, scrubland and barren terrain. The outcome of this work has been to add significant chronological resolution to the current map of Greater Angkor.