Archaeological Prospection And Defense Reconstruction Of The Cultural Landscape Of Yumen-yang Pass Using Spaceborne SAR Data

Earth Observation(EO)technologies including Visible/Infrared(VIR),the Airborne Laser Ranging and Measurement(Li DAR)and Synthetic Aperture Radar(SAR)have promoted the innovation of archaeological technology.Compared with other EO technologies,the spaceborne SAR technology,with advantages of all-day,all-weather,penetration,polarization and interference,provides a new viewpoint for investigating discovering and reconstructing the archaeological sites and cultural heritages.Both intensity and phase information contributes to form unique marks for surface archaeological remains.With the emergence of the second generation spaceborne SAR system,multi-source,multi-temporal and multi-mode spaceborne SAR has gradually become one of the most valuable data sources for remote sensing archaeology.Yumen and Yang passes,as the gateways of Hexi Corridor leading respectively the South and North route of the Silk Road to the Western Regions,are the two most important transportation and strategic hinges.In the Yumen-Yang Great site,at the edge of the Kumtag desert,restricted by the geographical span,the poor natural environment and the spectral analytical difficulty,there are still numerous unsolved mysteries in the tilling scope of ancient oasis,the location of southern defense line and the Yang pass.Considering the uniqueness of detection ability and scene reconstruction with the spaceborne SAR,combing the characteristics of the study area,the dissertation focued on the spaceborne SAR spatial archaeological methods and advanced demonstration study from three perspectives:extraction of ancient drainage system and ancient army farmland sites,extraction and prediction of archaeological targets in the forms of points,lines and plane surfaces,and reconstruction of the defense system.The main research work includes:Firstly,starting with the basic principles of radar archaeology,the basic principles and methods of spaceborne SAR archaeology were studied.Based on the radar geometry,main parameters of radar system,backscattering characteristics,bands of spaceborne SAR and the I&II generation spaceborne SAR systems,the mechanism of recognition of surface micro-topography,vegetation and soil archaeological marks on spaceborne SAR images was analyzed.The scattering characteristics of archaeological targets in the forms of point-line-surface,and the correlation with the surface morphology and dielectric properties were discussed with cases.The ideal penetration depths of spaceborne SAR with different wavelengths and incident angles on sandy surface were calculated and simulated.In terms of phase and intensity information extraction,space-borne SAR archaeological methods including interferometry and geomorphological reconstruction,enhancement and extraction of the weak archaeological marks were introduced.Secondly,at the landscape scale,with the landform reconstruction and vegetation mark identification abilities of Spaceborne SAR,scene information extraction and archaeological discovery of ancient drainage system-army farmland using Spaceborne SAR were carried out.The extraction methods and data processing work flow were proposed,studied and verified.For extracting ancient drainage system,a method integrating DEM extraction,digital terrain analysis,hydrological analysis and classification threshold was suggested.In view of the ancient farmland extraction,the vegetation archaeological mark were identified and a method of locating the ancient farmland areas of archaeological interest based on time-series PALSAR-1 intensity feature extraction and coherence constraints was introduced.The weighted DEM extraction method based on NL(Non local)-In SAR coherence coefficient unbiased estimation with TSX/TDX,and the digital terrain factors extraction were adopted to restore paleorivers(westbound Wulujian river and the upstream of Shangbanao etc.),estimate the ranges of marshlands(Daze)and paleolakes(Wowachi,etc.),and locate the potential farmland targets for garrison.The farmland target at the downstream of Xitugou was discovered for the first time with abandoned ditches extracted using spaceborne SAR.Thirdly,at the site scale,with the micro-topography sensitivity of II VHR SAR,archaeological target extraction and site prediction for Yumen-Yang Great site using spaceborne SAR were carried out.The extraction methods and work flow including existing site modelling,SAR imaging simulation and archaeological target extraction were proposed,studied and verified.A strong scattering and highly coherent scatters(SHS)extraction method for beacon tower candidate points with temporal series of Sentinel-1 images was considered,and a prior-knowledge based template matching method(PMTM)was put forward for extraction of the linear walls or trenches of Great Wall.With all the extracted results using the spaceborne SAR,a spatial multi-scale optimized BLR site prediction model with buffer constraints was finally proposed for site detection.The methods were applied to analyze the main archaeological targets in the forms of the points and lines in the study area.Based on the feature(size,material,preservation status and surrounding landforms)statistics of of the remains and the SAR imaging simulation,the site identification ability with multi-source and multi-mode SAR data(including incident angle and resolution)was discussed.Through the extraction method,the beacon tower candidate points were extracted and the Great Wall trenches in the north-south direction was precisely located.The extracted topographic factors,geometric and topological characteristics and stable dihedral angle scattering characteristics of point targets were finally put into the optimized site prediction model to assist field discovery of three Han Dynastic beacons:newly named as the Nanhu Beacon tower,the Nanhu 3^rd and the Nanhu 4^th beacon towers.Fouthly,the three-dimensional defense system reconstruction at the Yumen-Yang great site was carried out by integrating the landscape and site studies with archaeological documents.On one hand,the Han Great Wall defense system including the beacon tower subsystem,the wall subsystem and the trench subsystem was reconstructed;based on the reconstruction results,the location of Yang pass and its seat of the general was quantitatively estimated using multiple buffer zones analysis;on the other hand,the ancient drainage system-army farmland environment of Yumen-Yang Great site was reconstructed by combining historical documents and field campaigns.The temporal and spatial evolution of water environment and cultivated land was analyzed,and the largest cultivated area of Nanhu Oasis,where the ancient Yang Frontier pass was located,was obtained.It was the concluded that the ancient cultivated area was nearly double of that of today.The main contributions and innovations of the study were listed as follows:For the first time,both methods of the landscape archaeology and site archaeology with spaceborne SAR were proposed for Yumen-Yang Great site area and integrated to realize the reconstruction of local defense system.Applications showed that multi-source spaceborne SAR data,including sequential C-band Sentinel-1 and L-band PALSAR-1,different modes and high-precision TSX/TDX,are practical in archaeological target recognition,environment reconstruction and site exploration.Based on the research on the extraction of archaeological targets and the reconstruction of defense system,the original characteristics of the Great Wall,garrison farmlands and beacon towers of Han Dynasty were revealed,which provided a methodological reference for the discovery,automatic identification and extraction,digital reconstruction and human-land relationship recognition of archaeological sites.The research also has important scientific significance for the study of the changes of the frontier passes,the prosperity and declines of the ancient oases,the environmental evolution and the construction of ancient frontier defense,and provides the basis and scientific support for the protection of Silk Road Heritage Site.