Reconstruction of building façades using spaceborne multiview TomoSAR point clouds

In this paper we present an approach that allows automatic reconstruction of building façades from 4D point cloud generated from tomographic SAR processing. The approach is modular and works by extracting façade points from the point density projected onto the ground plane. Individual façades are segmented using an unsupervised clustering procedure. Surface (flat or curved) model parameters of the segmented building façades are further estimated and finally the geometric primitives such as intersection points of the adjacent façades are determined to complete the reconstruction process. The proposed approach is illustrated and validated by examples using TomoSAR point clouds generated from TerraSAR-X high resolution spotlight images

MONITORING AND EVALUATION OF A LONG-SPAN RAIWAY BRIDGE USING SENTINEL-1 DATA

This paper is focused on displacement monitoring of a bridge, which is one of the key aspects of its structural health monitoring. A simplified Persistent Scatterer Interferometry (PSI) approach is used to monitor the displacements of the Nanjing Dashengguan Yangtze River High-speed Railway Bridge (China). This bridge is 1272 m long and hosts a total of 6 railway lines. The analysis was based on a set of twenty-nine Sentinel-1A images, acquired from April 2015 to August 2016. A dense set of measurement points were selected on the bridge. The PSI results show a maximum longitudinal displacement of 150 mm, on each side of the bridge. The displacements are strongly correlated with the temperature, showing that they are due to thermal expansion. Using the PSI results, the Coefficient of Thermal Expansion (CTE) of the whole bridge was estimated. The result agrees well with the CTE of the bridge materials. Using a regression model, the PSI-measured displacements were compared with in-situ measurements. The paper proposes a procedure to assess the performance of the movable bearings of the bridge, which is based on the PSI measurements

ANALYSIS OF X-BAND VERY HIGH RESOLUTION PERSISTENT SCATTERER INTERFEROMETRY DATA OVER URBAN AREAS

Persistent Scatterer Interferometry (PSI) is a satellite-based Synthetic Aperture Radar (SAR) remote sensing technique used to measure and monitor land deformation from a stack of interferometric SAR images. This work concerns X-band PSI and, in particular, PSI based on very high resolution (VHR) StripMap CosmoSkyMed and TerraSAR-X SAR imagery. In fact, it mainly focuses on the technical aspects of deformation measurement and monitoring over urban areas. A key technical aspect analysed in this paper is the thermal expansion component of PSI observations, which is a result of temperature differences in the imaged area between SAR acquisitions. This component of PSI observations is particularly important in the urban environment. This is an interesting feature of PSI, which can be surely used to illustrate the high sensitivity of X-band PSI to very subtle displacements. Thermal expansion can have a strong impact on the PSI products, especially on the deformation velocity maps and deformation time series, if not properly handled during the PSI data processing and analysis, and a comprehensive discussion of this aspect will be provided in this paper. The importance of thermal expansion is related to the fact that the PSI analyses are often performed using limited stacks of images, which may cover a limited time period, e.g. several months only. These two factors (limited number of images and short period) make the impact of a non-modelled thermal expansion particularly critical. This issue will be illustrated considering different case studies based on TerraSAR-X and CosmoSkyMed PSI data. Besides, an extended PSI model which alleviates this problem will be described and case studies from the Barcelona metropolitan area will demonstrate the effectiveness of the proposed strategy

Measuring thermal expansion using X-band Persistent Scatterer Interferometry

This paper is focused on the estimation of the thermal expansion of buildings and infrastructures using X-band Persistent Scatterer Interferometry (PSI) observations. For this purpose an extended PSI model is used, which allows separating the thermal expansion from the total observed deformation thus generating a new PSI product: the map of the thermal expansion parameter, named thermal map. The core of the paper is devoted to the exploitation of the information contained in the thermal maps: three examples are discussed in detail, which concern a viaduct, a set of industrial buildings and two skyscrapers. The thermal maps can be used to derive the thermal expansion coefficient of the observed objects and information on their static structure. In addition, the paper illustrates the distortions in the PSI deformation products that occur if the thermal expansion is not explicitly modelled. Finally, an inter-comparison exercise is described, where the thermal expansion coefficients estimated by PSI are compared with those derived by a Ku-band ground-based SAR campaign

The PSIG procedure to Persistent Scatterer Interferometry (PSI) using X-band and C-band Sentinel-1 data

A new approach to Persistent Scatterer Interferometry (PSI) data processing and analysis implemented in the PSI chain of the Geomatics (PSIG) Division of CTTC is used in this work. The flexibility of the PSIG procedure allowed evaluating two different processing chains of the PSIG procedure. A full PSIG procedure was implemented in the TerraSAR-X dataset while a reduced PSIG procedure was applied to the nine Sentinel-1 images available at the time of processing. The performance of the PSIG procedure is illustrated using X-band and C-band Sentinel-1 data and several examples of deformation maps covering different types of deformation phenomena are shown. \ua9 (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Building deformation assessment by means of Persistent Scatterer Interferometry analysis on a landslide-affected area: the Volterra (Italy) case study

In recent years, space-borne InSAR (interferometric synthetic aperture radar) techniques have shown their capabilities to provide precise measurements of Earth surface displacements for monitoring natural processes. Landslides threaten human lives and structures, especially in urbanized areas, where the density of elements at risk sensitive to ground movements is high. The methodology described in this paper aims at detecting terrain motions and building deformations at the local scale, by means of satellite radar data combined with in situ validation campaigns. The proposed approach consists of deriving maximum settlement directions of the investigated buildings from displacement data revealed by radar measurements and then in the cross-comparison of these values with background geological data, constructive features and on-field evidence. This validation permits better understanding whether or not the detected movements correspond to visible and effective damages to buildings. The method has been applied to the southwestern sector of Volterra (Tuscany region, Italy), which is a landslide-affected and partially urbanized area, through the use of COSMO-SkyMed satellite images as input data. Moreover, we discuss issues and possible misinterpretations when dealing with PSI (Persistent Scatterer Interferometry) data referring to single manufactures and the consequent difficulty of attributing the motion rate to ground displacements, rather than to structural failures

Multi-Temporal Evaluation of Landslide Movements and Impacts on Buildings in San Fratello (Italy) By Means of C-Band and X-Band PSI Data

This work provides a multi-temporal and spatial investigation of landslide effects in the San Fratello area (Messina province within the Sicily region, Italy), by means of C-band and X-band Persistent Scatterer Interferometry (PSI) data, integrated with in situ field checks and a crack pattern survey. The Sicily region is extensively affected by hydrogeological hazards since several landslides regularly involved local areas across time. In particular, intense and catastrophic landslide phenomena have recently occurred in the San Fratello area; the last event took place in February 2010, causing large economic damage. Thus, the need for an accurate ground motions and impacts mapping and monitoring turns out to be significantly effective, in order to better identify active unstable areas and to help proper risk-mitigation measures planning. The combined use of historical and recent C-band satellites and current X-band Synthetic Aperture Radar sensors of a new generation permits spatially and temporally detection of landslide-induced motions on a local scale and to properly provide a complete multi-temporal evaluation of their effects on the area of interest. PSI ground motion rates are cross-compared with local failures and damage of involved buildings, recently recognized by in situ observations. As a result, the analysis of landslide-induced movements over almost 20 years and the validation of radar data with manufactured crack patterns, permits one to finally achieve a complete and reliable assessment in the San Fratello test site