SARchaeological Prospection: Synthetic Aperture Radar for the Reconstruction and Mapping of Temperate Floodplain Environments

Abstract

Temperate river floodplains present a significant challenge for archaeologists, as cultural and palaeoenvironmental remains are often difficult to locate but can be exceptionally well preserved, especially where groundwater levels are high. In these alluvial environments, the deposition of thick, fine-grained sediments has potential to deeply bury rich archaeological archives that can be used to reconstruct past environments, but these deposits also render conventional forms of archaeological prospection largely ineffective. Consequently, subsurface mapping techniques have been developed to determine the three-dimensional spatial distribution of archaeological remains and their relationship to sediment architecture within alluvial environments. These can be generated using a combination of intrusive (boreholes, trial pits, etc.) and nonintrusive (e.g., geophysical survey) investigations augmented by other geological and topographical datasets. Although lidar and other passive remote sensing methods such as multispectral imagery and aerial photography have been utilized to investigate floodplain landscapes, the spaceborne capabilities of Synthetic Aperture Radar (SAR) have yet to be explored within the context of geoarchaeological prospection. This contribution, therefore, examines the capacity of SAR to reconstruct and map landform assemblages within temperate river floodplains by analysing images in a 6-year time series of (COSMO-SkyMed) SAR data across two valleys in Herefordshire, United Kingdom. The results demonstrate that SAR can be used to record the spatial extent of recent flood events to outline surface topographic complexity and water table levels to achieve a detailed understanding of subsurface complexity across temperate river floodplains. This information can, in turn, be used to form a ‘model’ of the likely distribution and potential preservation conditions of archaeological resources. Although higher resolution topographic datasets (e.g., lidar, if available) may often be more effective, the integration of SAR within geoarchaeological investigations provides an alternative data source for the reconstruction of alluvial landscapes.