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Summary of Proposal CAL2073

TitleThe Potential of TerraSAR-Xfor Monitoring the Defected Deformation around the World Heritage of Angkorsite, Cambodia
Investigator Chen, Fulong - Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth
Team Member
Prof. Ishwaran, Natarajan - International Centre on Space Technologies for Natural and Cultural Heritage und, The Institute of Remote Sensing and Digital Earth
Assistant Prof. Zhou, Wei - International Centre on Space Technologies for Natural and Cultural Heritage und, The Institute of Remote Sensing and Digital Earth
Dr. HANG, Peou - APSARA National Authority, Cambodia, APSARA
SummaryThe deformation monitoringin Angkor site will be a significant tool in interpreting the potential causesthat threaten the collapse ancient temples. The primary scientific objective isto obtain high-resolution (3m StripMap), repeat pass TerraSAR-X data formeasuring the spatial-temporal evolution of ground displacement in Angkor site.The X-band observations will also be integrated and compared with the resultsderived from C-band ERS-1/2 as well as other ground-based measurements that willbe obtained during the implementation of RSEA project. The parameters ofmotions (single relic abnormal displacement, large-scale surrounding groundsubsidence) in spatial-temporal domain that will measured and monitored during this project will help to improve theunderstanding of past and potential future collapse events in Angkor site.
Final ReportSupported by the general AO project (CAL2073), the performance and capability of TerraSAR-X data for the World Heritage (Angkor site in this study) risking monitoring and sustainable development were implemented and assessed. Two case studies were conducted as follows: 1)Flood monitoring and change detetion: Flooding is one of significant hazards in the World Heritage of Angkor site. In this study, 28 scenes of TerraSAR-X images through the acquisition of 2011-2013 were selected for the water feature extraction and the flood monitoring. Taking the dry season acquisition of March 10 and flood season of October 16 in 2011, the performance of the three two-fold classification approaches, including Otsu, two-dimensional maximum entropy and the mixed threshold, were firstly compared using the grey-level amplitude SAR images. Compared with the result of Otsu (underestimation) and two-dimensional maximum entropy (overestimation), it is clear that the mixed threshold approach derives a moderate classification. For the significant factor analysis, the mixed threshold approach was applied for the water feature extraction and then the time series analysis using the 28 scenes selected TerraSAR-X images. The relationship between the water body expansion/shrinkage and the precipitation was further investigated. Results demonstrated that the seasonal or annual variation of water bodies in Angkor was impacted by the precipitation, indicating a consistent trend for the water body expansion and the precipitation rising in flood seasons. After that, the linear regression model was applied for the quantitative analysis. Results shown that although not significant, there is a positive linear correlation between the variation of the monthly precipitation and the water bodies extracted, indicated by the coefficients of 0.077 in 2011, 0.132 in 2012 and 0.054 in 2013, respectively. This low correlation can be interpreted from two-folds. i) It implied that there are other factors linked to the occurrence of floods in Angkor site, such as the downstream runoff of Mekong River and the water level rise of Tonle Sap Lake, apart from the local precipitation. ii) The difference of SAR and precipitation data in aspects of temporal sampling and spatial resolution induces measurement alias. 2)Radar interferometry offers new insights into threats to the Angkor site: As the legacy from the past and the common wealth to future generations,heritage is essential for social development and transmission of cultural identity. Nowadays, sustainability of World Heritage sites faces a number of challenges from aggravated modern anthropogenic activities coupled with rapidly changing landscapes. Earth Observation technology provides a feasible platform for monitoring and conservation of heritage, considering its capability for synoptic and objective assessments. In this study, we measured the impacts of hitherto imperceptible and poorly understood factors of groundwater and temperature variations on the monuments in the Angkor World Heritage site (400 km2). We developed a two-scale synthetic aperture radar interferometry(InSAR) approach. We describe spatial-temporal displacements (at millimeter-level accuracy), as measured by high-resolution TerraSAR/TanDEM-X satellite images, to provide a new solution to resolve the current controversy surrounding the potential structural collapse of monuments in Angkor. Multidisciplinary analysis in conjunction with a deterioration kinetics model offers new insights into the causes that trigger the potential decline of Angkor monuments. Our results show that pumping groundwater for residential and touristic establishments did not threaten the sustainability of monuments during 2011 to 2013; however, seasonal variations of the groundwater table and the thermodynamics of stone materials are factors that could trigger and/or aggravate the deterioration of monuments.These factors amplify known impacts of chemical weathering and biological alteration of temple materials. The InSAR solution reported in this study could have implications for monitoring and sustainable conservation of monuments in World Heritage sites elsewhere.

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