Deodato Tapete

Satellite radar interferometry for monitoring and early-stage warning of structural instability in archaeological sites

Satellite interferometric synthetic aperture radar (InSAR) monitoring campaigns were performed on the archaeological heritage of the Roman Forum, Palatino and Oppio Hills in the centre of Rome, Italy, to test the capabilities of persistent scatterer interferometry techniques for the preventive diagnosis of deformation threatening the structural stability of archaeological monuments and buried structures. ERS-1/2 and RADARSAT-1/2 SAR images were processed with the permanent scatterers InSAR (PSInSAR) and SqueeSAR approaches, and the identified measurement points (MP) were radar-interpreted to map the conservation criticalities in relation to the local geohazard factors and active deterioration processes. The multi-temporal reconstruction of past/recent instability events based on the MP deformation time series provided evidences of stabilization for the Domus Tiberiana as a consequence of recent restoration works, as well as of persistent deformation for the Temple of Magna Mater on the Palatino Hill and the structures of the Baths of Trajan on the Oppio Hill. Detailed time series analysis was also exploited to back monitor and understand the nature of the 2010 collapse that occurred close to Neros Golden House, and to establish an early-stage warning procedure useful to preventively detect potential instability.

Rapid Mapping and Deformation Analysis over Cultural Heritage and Rural Sites Based on Persistent Scatterer Interferometry

We propose an easy-to-use procedure of “PSI-based rapid mapping and deformation analysis,” to effectively exploit Persistent Scatterer Interferometry (PSI) for multispatial/temporal hazard assessment of cultural heritage and rural sites, update the condition report at the scale of entire site and single building, and address the conservation strategies. Advantages and drawbacks of the methodology are critically discussed based on feasibility tests performed over Pitigliano and Bivigliano, respectively, located in Southern and Northern Tuscany, Italy, and representative of hilltop historic towns and countryside settlements chronically affected by natural hazards. We radar-interpreted ERS-1/2 (1992–2000) and ENVISAT (2003–2010) datasets, already processed, respectively with the Permanent Scatterers (PSs) and Persistent Scatterers Pairs (PSPs) techniques, and assigned the levels of conservation criticality for both the sites. The PSI analysis allowed the zoning of the most unstable sectors of Pitigliano and showed a good agreement with the most updated hazard assessment of the cliff. The reconstruction of past/recent deformation patterns over Bivigliano confirmed the criticality for the Church of San Romolo, supporting the hypothesis of a correlation with local landslide phenomena, as also perceived from the annual motions observed over the entire site, where several landslide bodies are mapped.

A User-Oriented Methodology for DInSAR Time Series Analysis and Interpretation: Landslides and Subsidence Case Studies

Recent advances in multi-temporal Differential Synthetic Aperture Radar (SAR) Interferometry (DInSAR) have greatly improved our capability to monitor geological processes. Ground motion studies using DInSAR require both the availability of good quality input data and rigorous approaches to exploit the retrieved Time Series (TS) at their full potential. In this work we present a methodology for DInSAR TS analysis, with particular focus on landslides and subsidence phenomena. The proposed methodology consists of three main steps: (1) pre-processing, i.e., assessment of a SAR Dataset Quality Index (SDQI) (2) post-processing, i.e., application of empirical/stochastic methods to improve the TS quality, and (3) trend analysis, i.e., comparative implementation of methodologies for automatic TS analysis. Tests were carried out on TS datasets retrieved from processing of SAR imagery acquired by different radar sensors (i.e., ERS-1/2 SAR, RADARSAT-1, ENVISAT ASAR, ALOS PALSAR, TerraSAR-X, COSMO-SkyMed) using advanced DInSAR techniques (i.e., SqueeSAR™, PSInSAR™, SPN and SBAS). The obtained values of SDQI are discussed against the technical parameters of each data stack (e.g., radar band, number of SAR scenes, temporal coverage, revisiting time), the retrieved coverage of the DInSAR results, and the constraints related to the characterization of the investigated geological processes. Empirical and stochastic approaches were used to demonstrate how the quality of the TS can be improved after the SAR processing, and examples are discussed to mitigate phase unwrapping errors, and remove regional trends, noise and anomalies. Performance assessment of recently developed methods of trend analysis (i.e., PS-Time, Deviation Index and velocity TS) was conducted on two selected study areas in Northern Italy affected by land subsidence and landslides. Results show that the automatic detection of motion trends enhances the interpretation of DInSAR data, since it provides an objective picture of the deformation behaviour recorded through TS and therefore contributes to the understanding of the on-going geological processes.

Rating health and stability of engineering structures via classification indexes of InSAR Persistent Scatterers

We propose a novel set of indexes to classify the information content of Persistent Scatterers (PS) and rate the health of engineering structures at urban to local scale. PS are automatically sampled and grouped via ‘control areas’ coinciding with the building and its surrounding environment. Density over the ‘control areas’ and velocity of PS are converted respectively into: Completeness of Information Index (Ici) that reflects the PS coverage grade; and Conservation Criticality Indexes (Icc) which rate the health condition of the monument separately for the object and surrounding control areas. The deformation pattern over the structure is classified as isolated (i) or diffused (d) based on the Velocity Distribution Index (Ivd). Both Ici and Icc are rated from A to E classes using a colour-coded system that intentionally emulates an energy-efficiency scale, to encourage the exploitation of PS by stakeholders and end-users in the practise of engineering surveying. Workability and reliability of the classification indexes are demonstrated over the urban heritage of Florence, Italy, using well established ERS-1/2 (1992–2000) descending, ENVISAT (2003–2010) ascending and descending PS datasets. The indexes are designed in perspective of handling outputs from InSAR processing of higher-resolution time series.

Radar Interferometry for Early Stage Warning on Monuments at Risk

Prevention measures on monuments affected by landslides and instability processes can effectively avoid damages to the elements at risk if the warning phase takes place at an ‘early stage’, i.e. when the phenomena are not completely triggered and developed. To realize this warning approach, satellite and ground-based radar interferometry techniques were tested, exploring their capabilities for detection and monitoring of structural deformation on the monuments of archaeological areas in Rome (Italy). Thanks to a procedure shared with the local conservators, fully involved in both investigation and feedback phases, early stage warning was carried out. Updated mapping products were obtained, identifying the most critical sectors to be stabilized. The recognition of definite deformation patterns allowed a high level of alert to be activated because of the significant threat for the monument conservation and public safety. Temporal series analysis highlighted the onset of probable instability processes, suggesting appropriate mitigation countermeasures.

Structural Assessment of Case Study Historical and Modern Buildings in the Florentine Area Based on a PSI-Driven Seismic and Hydrogeological Risk Analysis

C-band medium-resolution Persistent Scatterer Interferometry (PSI) data from ERS-1/2, ENVISAT and RADARSAT-1 were used to establish a classification method preparatory to seismic and hydrogeological risk assessment of historical buildings in urban areas. Tests were conducted over the heritage city of Florence, Italy, using a multidisciplinary approach which takes into account geological and environmental factors of hazards, along with parameters related to conservation history of the monuments and the possible sources of damage commonly found within an urban context. The case study herein presented confirm the advantages of PSI against its well-known limitations, and demonstrate how PSI can be used to support subsequent structural analyses of buildings.

Correlation between erosion patterns and rockfall hazard susceptibility in hilltop fortifications by terrestrial laser scanning and diagnostic investigations

A holistic methodology combining conventional diagnostic investigations and kinematic analysis performed on 3D laser scanning survey is here proposed for rockfall hazard assessment and erosion patterns study, to map critical sectors and evaluate potential impacts on the conservation of cultural heritage sites built on unstable rock masses. Experiments carried out on the fortifications of Citadel, Gozo (Malta), led us to classify the susceptibility of the cliff surfaces to instability mechanisms, recognizing the wedge failure as the highest hazardous one. Observations on thin section of the rock textural properties and measurements of the resistance to abrasion completed the laser-based analysis, clarifying the intrinsic weakness of the outcropping limestones. Levels of conservation criticality were assigned to the rock mass sectors located underneath the historical buildings, and on site monitoring system was installed to follow the evolution of the crack patterns.

InSAR data for geohazard assessment in UNESCO World Heritage sites: state-of-the-art and perspectives in the Copernicus era

Abstract Protection of natural and cultural heritage is encompassed by the United Nations’ 2030 Agenda for Sustainable Development and is among the innovative applications and services of the European Union’s Earth Observation programme Copernicus. We are currently witnessing an increasing exploitation of Interferometric Synthetic Aperture Radar (InSAR) methods to assess geohazards affecting cultural heritage. This paper offers the first data mining exercise to identify InSAR geoinformation that is digitally available and/or published and that spatially includes one or more cultural, natural and mixed UNESCO World Heritage Site (WHS). The exercise focused on the 45 countries of geographical Europe, Turkey, Israel and the Russian Federation, and their 445 WHS of Outstanding Universal Value. We built a database of academic and grey literature collated via a Boolean search of the ISI Web of Science catalogue and systematic skim-reading to a total number of 280 publications as of the end of 2016. Over 460 InSAR open access digital datasets were also analysed. We found clusters of WHS covered by InSAR data in Italy, the Netherlands, western Germany, eastern Spain, Greece and the UK that match with the geographic distribution of InSAR expertise and geohazard hotspots. The existing stock of InSAR geoinformation already provides an overall WHS coverage of 36%, with similar proportion of available data for ‘urban’ (40%) and ‘rural’ (34%) WHS. The sites with the highest number of publications are historic city centres (e.g. Amsterdam, Athens, Barcelona, Lisbon, Paris, Rome), as well as Permanent Geohazard Supersites (e.g. Mt. Etna, Naples, Istanbul), where the impact of natural and/or anthropogenic processes is well known. First generation SAR data (mainly ERS-1/2) predominate in the literature with over 15 new publications/year since 2002, whilst second and third generation data show less pronounced rates since 2007 and 2014, respectively. The current engagement level of end-users appears still limited (less than 1% of publications involve heritage stakeholders), and a shared guidance on the use of InSAR for heritage practitioners does not exist yet. Towards the development of Copernicus’ services and applications in support of cultural heritage preservation and management, our analysis contributes to: outline the existing capabilities; focus on requirements for bespoke InSAR-derived products and services; and consider possible implementation scenarios both in emergency and ordinary circumstances.

Multi-Temporal Evaluation of Landslide-Induced Movements and Damage Assessment in San Fratello (Italy) by Means of C- and X-Band PSI Data

This work provides a valuable multi-temporal and spatial investigation of landslide effects in San Fratello area (Messina province, Sicily Region, Italy), by means of C-/X-band PSI (Persistent Scatterer Interferometry) data, integrated with in-situ field checks and crack pattern survey. In February 2010 a catastrophic landslide caused casualties and large economic damages. Thus, an accurate mapping and monitoring of ground motions and impacts turn out to be significantly effective. PSI ground motion rates were cross-compared with local failures and displacement features of single buildings observed in-situ. Landslide-induced motions were detected at local scale over almost 20 years, with a validation of radar data and manufactures crack patterns, to finally achieve a complete and reliable assessment.

Testing Computational Methods to Identify Deformation Trends in RADARSAT Persistent Scatterers Time Series for Structural Assessment of Archaeological Heritage

RADARSAT-1 data stacks processed by means of Persistent Scatterer Interferometry (PSI) over the central archaeological area of Rome, Italy, and radar-interpreted according to the procedure of radar mapping by Tapete and Cigna (2012), were re-analyzed by applying the Deviation Index DI1 defined by Cigna et al. (2012). Our tests aimed to assess how an early computational identification of deformation trends within the displacement time series can support strategies of preventive conservation. The suitability of such semi-automated method for trend recognition is discussed with regard to a traditional approach of manual check of PSI time series, at the scale of single measurement point. Results from the case studies of Palatine and Oppian Hills are presented in this paper, examining both advantages and drawbacks offered by the implementation of such type of computational approach.