SAR-based detection of buried ruins: present possibility and uncertainties

Abstract:

Investigation of sub-ground heritages of ancient building is an essential research activity to discuss global environmental changes affecting human civilization. Numerous efforts are needed to identify a new archeological site, which is buried in soil and/or sand. Multiple previous studies suggested that sub-ground archaeological sites is identifiable by microwave penetration which is emitted and received by space-borne Synthetic Aperture Radar (SAR). However, previously-performed few cases of archaeological-site detection did not consider topographic effects (i.e. relative surface angle toward the SAR antenna).

In this study, therefore, SAR data (JERS-1 and PALSAR) and a digital surface model (AW3D30: ALOS World 3D -30 m) were used to validate SAR-based detection of sub-ground heritage sites No.29 and No.39 in Saqqara, Egypt. We found that the backscatter of the buried ruins has unignorable uncertainty, because similar backscatter is caused at the surrounding landforms. A possible reason is that similar backscattering coefficient trends may be obtained, when the landform has the similar slope and slope direction. We compared backscatter coefficient between the buried ruins and surrounding landform. As a result, the backscattering coefficient of the Site No.29 in the JERS-1/SAR image, ALOS PALSAR FBS (HH) mode multitemporal mean backscatter image and the ALOS PALSAR PLR mode 2007 (HH) backscatter image tended to be higher than the backscattering coefficient of the surrounding landforms which had the similar slope and slope detection. This result suggests that the backscatter around Site No.29 on these images may be the backscatter of the buried ruins. Compared with the JERS-1 image, ALOS PALSAR images are difficult to detect Site No.29. Our present method did not consider the influence of surface roughness, observation mode, incident angle, and small satellite line-of-sight. In the next study, we will focus on the influence of surface roughness to distinguish the backscatter of the buried ruins from the backscatter of the surface roughness.