SAR polarimetry for archaeology. Multi-frequency analysis over the UNESCO site of Gebel Barkal, Sudan

The present research aims to exploit the technique of SAR Polarimetry for the detection of surface and subsurface archaeological structures, comparing ALOS PALSAR L-band (central frequency 1.27 GHz), with RADARSAT-2 C-band sensor (central frequency 5.405 GHz). The great potential of the two polarimetric sensors with different frequency for the detection of archaeological remains has been demonstrated thanks to the sand penetration capability of both C-band and L-band sensors. Differences in vegetation growth and in soil moisture content generate ground anomalies which can be linked to subsurface anthropic structures. Such evidences have been studied by means of aerial photographs and of historical II World War acquisitions first, and of very high spatial resolution of optical satellites later. The choice to analyse radar sensors is based on their 24-hour observations, their independence from an external illumination source (Sun) and from meteorological conditions. Moreover, they can provide additional information about the electromagnetic properties of the target, not derivable from optical images. Polarimetric SAR data where analysed with PolSARpro software. All the products were then analysed simultaneously with ancillary information and optical satellite data, used as a basis for the georeferencing process. The perfect geographic correspondence between data constitutes a fundamental step in archaeological researches for a correct interpretation of the scattering mechanisms of ancient structures and their interaction with surrounding areas.