Detection of Archaeological Residues in Vegetated Areas Using Satellite Synthetic Aperture Radar

Buried archaeological structures, such as earthworks and buildings, often leave traces at the surface by altering the properties of overlying material, such as soil and vegetation. These traces may be better visible from a remote perspective than on the surface. Active and passive airborne and spaceborne sensors acquiring imagery from the ultraviolet to infrared have been shown to reveal these archaeological residues following the application of various processing techniques. While the active microwave region of the spectrum, in the form of Synthetic Aperture Radar (SAR) has been used for archaeological prospection, particularly in desert regions, it has yet to be fully exploited to detect buried structures indirectly though proxy indicators in overlying materials in vegetated areas. Studies so far have tended to focus on the intensity of the SAR signal, without making full use of the phase. This paper demonstrates that SAR backscatter intensity, coherence and interferometry can be used to identify archaeological residues over a number of areas in the vicinity of Rome, Italy. SAR imagery from the COnstellation of small Satellites for the Mediterranean basin Observation (COSMO-SkyMed) have been obtained for the analysis: 77 scenes in Stripmap and 27 in Spotlight mode. Processing included multitemporal speckle filtering, coherence generation and Digital Elevation Model (DEM) creation from Small Baseline Subsets (SBAS). Comparison of these datasets with archaeological, geological, soil, vegetation and meteorological data reveal that several products derived from SAR data can expose various types of archaeological residues under different environmental conditions.