Angkor Underground - Applying GPR to analyse the diachronic structure of a great urban complex

This thesis is based on surveys of ground-penetrating radar (GPR) conducted at Angkor, Cambodia. The appraisal of preceding remote sensing surveys led to selective ground based prospection for archaeological objects of interest on different scales. The successive relocation of the political and religious centre from the 9th to the 14th century has left a palimpsest landscape that reaches from small artificial habitation mounds, masonry monuments and their enclosures, to the extensive water management network of channels and earthworks that covered large parts of the floodplain between the Kulen Hills and Lake Tonle Sap. To make efficient use of the technique, the GPR survey had to be adjusted to those dimensions. The area-covering grid method was chosen for small scale surveys on habitation patterns, production sites and cemeteries, testing potential and limits in the application. A major factor in the measuring and processing of data was the floodplain geology of predominantly clayey sand and an environment prone to inundation that provided varying signal penetration depths depending on either compact or soft soil. For the larger scales, GPR was used in combination with GPS, GIS and remote sensing data sets. The concept of spatial configuration of monuments in and outside of enclosures led the search for remains of missing laterite and sandstone structures. A survey in the centre of Angkor Wat revealed the outline of six towers as part of a potential quincunx formation. They were further analysed by excavations to establish a preliminary construction history of the area. Surveys inside the peripheral enclosures of Chau Srei Vibol, Banteay Sra and Prasat Komnap showed evidence of demolished structures, some of it possibly from the Angkorian period. For questions concerning the functioning of a water management system in the Angkorian floodplain, GPR profiles in search for infrastructure were conducted alongside and over the embankments of the giant reservoirs. Evidence of outlets in the central areas of the eastern embankments of all four baray at Angkor confirmed them being part of the network. On the largest scale, GPR transects were run across parts of the floodplain to investigate the network of canals and earthworks that had been mapped by remote sensing. Obstacles, profiles and grids as well as the detected anomalies were integrated into a geo-referenced GIS database. Potential connections between centres and temples were integrated at areas where associated and previously mapped earthworks discontinued. Anomalies associated to the water management features were classified according to their characteristics and potential function as former artificial and natural channels, moats, ponds as well as masonry remains, and analysed with regard to archaeological maps and available remote sensing data. Newly acquired high resolution satellite radar (TerraSAR-X) data was used to evaluate a potential relation between water saturation and anomalies. The complete dataset was analysed for a complementation of archaeological maps and with the intent to separate features of the artificial canal network of Angkor from the natural landscape and the original distribution of rivers