{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T01:05:58Z","timestamp":1773363958759,"version":"3.50.1"},"reference-count":29,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2017,4,15]],"date-time":"2017-04-15T00:00:00Z","timestamp":1492214400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Spaceborne Multi-Temporal Synthetic Aperture Radar (SAR) Interferometry (MT-InSAR) has been a valuable tool in mapping motion phenomena in different scenarios. Recently, the capabilities of MT-InSAR for risk monitoring and preventive analysis of heritage sites have increasingly been exploited. Considering the limitations of conventional MT-InSAR techniques, in this study a two-step Tomography-based Persistent Scatterers (PS) Interferometry (Tomo-PSInSAR) approach is proposed for monitoring ground deformation and structural instabilities over the Ancient City Walls (Ming Dynasty) in Nanjing city, China. For the purpose of this study we utilized 26 Stripmap acquisitions from TerraSAR-X and TanDEM-X missions, spanning from May 2013 to February 2015. As a first step, regional-scale surface deformation rates on single PSs were derived (ranging from \u221240 to +5 mm\/year) and used for identifying deformation hotspots as well as for the investigation of a potential correlation between urbanization and the occurrence of surface subsidence. As a second step, structural instability parameters of ancient walls (linear motion rates, non-linear motions and material thermodynamics) were estimated by an extended four-dimensional Tomo-PSInSAR model. The model applies a two-tier network strategy; that is, the detection of most reliable single PSs in the first-tier Delaunay triangulation network followed by the detection of remaining single PSs and double PSs on the second-tier local star network referring to single SPs extracted in the first-tier network. Consequently, a preliminary phase calibration relevant to the Atmospheric Phase Screen (APS) is not needed. Motion heterogeneities in the spatial domain, either caused by thermal kinetics or displacement trends, were also considered. This study underlines the potential of the proposed Tomo-PSInSAR solution for the monitoring and conservation of cultural heritage sites. The proposed approach offers a quantitative indicator to local authorities and planners for assessing potential damages as well as for the design of remediation activities.<\/jats:p>","DOI":"10.3390\/rs9040371","type":"journal-article","created":{"date-parts":[[2017,4,18]],"date-time":"2017-04-18T11:22:04Z","timestamp":1492514524000},"page":"371","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Surface Motion and Structural Instability Monitoring of Ming Dynasty City Walls by Two-Step Tomo-PSInSAR Approach in Nanjing City, China"],"prefix":"10.3390","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-1144-0004","authenticated-orcid":false,"given":"Fulong","family":"Chen","sequence":"first","affiliation":[{"name":"Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"},{"name":"International Centre on Space Technologies for Natural and Cultural Heritage under the Auspices of UNESCO, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"}]},{"given":"Yuhua","family":"Wu","sequence":"additional","affiliation":[{"name":"Chinese Academy of Cultural Heritage, No. 2 Gaoyuan Street Beisihuan Donglu, Chaoyang District, Beijing 100029, China"}]},{"given":"Yimeng","family":"Zhang","sequence":"additional","affiliation":[{"name":"Chinese Academy of Cultural Heritage, No. 2 Gaoyuan Street Beisihuan Donglu, Chaoyang District, Beijing 100029, China"}]},{"given":"Issaak","family":"Parcharidis","sequence":"additional","affiliation":[{"name":"Department of Geography, Harokopio University, 17671 Kallithea-Athens, Greece"}]},{"given":"Peifeng","family":"Ma","sequence":"additional","affiliation":[{"name":"Institute of Space and Earth Information Science, The Chinese University of Hong Kong, ShaTin, N.T., Hong Kong 999077, China"}]},{"given":"Ruya","family":"Xiao","sequence":"additional","affiliation":[{"name":"Department of Geomatics, School of Earth Science and Engineering, Hohai University, Nanjing 211100, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7073-0082","authenticated-orcid":false,"given":"Jia","family":"Xu","sequence":"additional","affiliation":[{"name":"Department of Geomatics, School of Earth Science and Engineering, Hohai University, Nanjing 211100, China"}]},{"given":"Wei","family":"Zhou","sequence":"additional","affiliation":[{"name":"Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"},{"name":"International Centre on Space Technologies for Natural and Cultural Heritage under the Auspices of UNESCO, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"}]},{"given":"Panpan","family":"Tang","sequence":"additional","affiliation":[{"name":"Key Laboratory of Digital Earth Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"},{"name":"International Centre on Space Technologies for Natural and Cultural Heritage under the Auspices of UNESCO, No. 9 Dengzhuang South Road, Haidian District, Beijing 100094, China"}]},{"given":"Michael","family":"Foumelis","sequence":"additional","affiliation":[{"name":"European Space Agency (ESA-ESRIN), Science, Applications and Future Technologies Department, Via Galileo Galilei, 00044 Frascati, Italy"}]}],"member":"1968","published-online":{"date-parts":[[2017,4,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1564","DOI":"10.3390\/rs6021564","article-title":"Slope superficial displacement monitoring by small baseline SAR interferometry using data from L-band ALOS PALSAR and X-band TerraSAR: A case study of Hong Kong","volume":"6","author":"Chen","year":"2014","journal-title":"Remote Sens."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1109\/36.898661","article-title":"Permanent scatterers in SAR interferometry","volume":"39","author":"Ferretti","year":"2001","journal-title":"IEEE Trans. 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