Semi-automated detection of surface degradation on bridges based on a level set method

Due to the effect of climate factors, natural phenomena and human usage, buildings and infrastructures are subject of progressive degradation. The deterioration of these structures has to be monitored in order to avoid hazards for human beings and for the natural environment in their neighborhood. Hence, on the one hand, monitoring such infrastructures is of primarily importance. On the other hand, unfortunately, nowadays this monitoring effort is mostly done by expert and skilled personnel, which follow the overall data acquisition, analysis and result reporting process, making the whole monitoring procedure quite expensive for the public (and private, as well) agencies. This paper proposes the use of a partially user-assisted procedure in order to reduce the monitoring cost and to make the obtained result less subjective as well. The developed method relies on the use of images acquired with standard cameras by even inexperienced personnel. The deterioration on the infrastructure surface is detected by image segmentation based on a level sets method. The results of the semi-automated analysis procedure are remapped on a 3D model of the infrastructure obtained by means of a terrestrial laser scanning acquisition. The proposed method has been successfully tested on a portion of a road bridge in Perarolo di Cadore (BL), Italy

A geodatabase for multisource data applied to cultural heritage: The case study of Villa Revedin Bolasco

In this paper we present the results of the development of a Web-based archiving and documenting system aimed to the management of multisource and multitemporal data related to cultural heritage. As case study we selected the building complex of Villa Revedin Bolasco in Castefranco Veneto (Treviso, Italy) and its park. Buildings and park were built in XIX century after several restorations of the original XIV century area. The data management system relies on a geodatabase framework, in which different kinds of datasets were stored. More specifically, the geodatabase elements consist of historical information, documents, descriptions of artistic characteristics of the building and the park, in the form of text and images. In addition, we used also floorplans, sections and views of the outer facades of the building extracted by a TLS-based 3D model of the whole Villa. In order to manage and explore these rich dataset, we developed a geodatabase using PostgreSQL and PostGIS as spatial plugin. The Web-GIS platform, based on HTML5 and PHP programming languages, implements the NASA Web World Wind virtual globe, a 3D virtual globe we used to enable the navigation and interactive exploration of the park. Furthermore, through a specific timeline function, the user can explore the historical evolution of the building complex

State of the Art of Ground and Aerial Laser Scanning Technologies for High-Resolution Topography of the Earth Surface

AbstractLaser scanners have increased their efficiency exponentially when compared to state of the art ten years ago. More data can be acquired—and higher accuracy can be achieved—over longer ranges thanks to advancements in sensor technology. The goal of this review is to present state of the art of terrestrial and aerial laser scanner surveys with a critical discussion over quality, which is a very important aspect for high-resolution topography

Comparison of discrete return and waveform terrestrial laser scanning for dense vegetation filtering

Abstract. In this paper we present the results of the comparison between two terrestrial laser scanners (TLS), a discrete return system (Riegl LMS-Z620) and an echo-digitizing system (Riegl VZ-400), employed for the survey of a dense forested area, in the italian Alps. The site is actually undergoing a strong debate among the inhabitants and local government authorities about the exploitation of the area as a huge quarry to produce building material. The dispute originates from the uncertainty about the instability of the underlying mountain slope, which was interested in 1966 by a landslide. The whole area was surveyed with the two laser scanners on February 2011 during the vegetation dormant period. A slight different processing workflow was applied to the collected datasets: the VZ-400 scans were pre-filtered by exploiting the "calibrated relative reflectance" readings and the multi-target capability provided by this laser scanning system. Next, two different spatial filters were applied to both the resulting georeferenced 3D models, in order to eliminate as much vegetation as possible: iterative filter and a custom morphological filter, developed by the authors. Achieved results show that for both datasets, the iterative and the morphological filters perform quite well for eliminating the vegetation, though some manual editing is still required since vegetation does not feature a prevalent growing direction. Furthermore, the comparison between the number of points left in the final DTMs shows that the VZ-400 provided a one order of magnitude denser point cloud wrt. the LMS-Z620. This demonstrates that a TLS with multi-target capability can potentially provide a more detailed DTM even in presence of dense vegetation

GENERATION OF INDOOR POINT CLOUDS EXPLOITING GEOMETRIC SYMMETRIES AND REGULARITIES

Abstract. 3D building modeling is becoming an important support in civil engineering, architecture and cultural heritage applications. Despite static laser scanning can be considered as the state-of-the-art in such kind of applications, mobile mapping techniques can be considered as a suitable alternative to quickly gather geospatial information. Outdoor mobile mapping can be considered as a mature technique, which takes into advantage of the Global Navigation Satellite System (GNSS)-laser scanning information fusion. Instead, indoor mobile mapping is typically more challenging: the unavailability of GNSS makes the mapping system rely either just on the inertial navigation system, or on some control points. A drift in the navigation solution, and consequently in the 3D reconstruction, is typically visible after a while in the former case, whereas the use of other surveying instruments is required in the latter.This work aims at exploiting geometric characteristics of the buildings, such as symmetries and regularities, to reduce the drift effect in indoor mobile mapping, in particular when dealing with affordable systems. The proposed approach is based on the segmentation of the point clouds acquired with a time of flight camera (ToF), detecting in particular vertical planar surfaces. It is well known that aligning planar surfaces can be a viable way for reducing the drift in this kind of applications. Nevertheless, this paper aims also at investigating the use of geometric symmetries to such aim.The proposed approach is tested on a case study, a building of the University of Padova, whose reconstruction was produced by an ad hoc affordable mobile mapping system, integrating low cost inertial sensors, RGB and ToF camera

A Real Multitechnology Microgrid in Venice: A Design Review

Electrical grids are evolving rapidly toward smart, self-regulating systems capable of managing distributed generation from intermittent renewable sources. Apart from hydroelectric, the large majority of them are photovoltaic (PV) systems grasping the fluctuating solar radiation and wind turbines (WT) capturing fickle wind energy, but other sources, which are at different stages of development, also generate energy with predictable or unpredictable intermittency. Several investigations have highlighted that, when power production from intermittent sources exceeds 20% of the total generation, the grid may face instabilities that can evolve into blackouts. Energy storage (ES) is a measure to balance source-load mismatches and to avoid such occurrence, but it can also provide a number of additional services which are part of the smart-grid paradigm. The operation of energy storage systems (ESSs) depends on the interface converters that manage the power flow and on the supervisors that control them according to the ESS, grid, and load features. Furthermore, the transmission system operator (TSO) may impose constraints on the ESS operation such as the obligation of contributing to primary regulation. Several numerical analyses have been developed to investigate the behavior of electrical grids provided with energy generation from renewable sources and energy storage, either islanded or connected to the national/transnational grid (macrogrid)

Thermal signature reduction through liquid nitrogen and water injection

The protection of aircraft against shoulder fired heat seeking missiles is of growing concern in the aviation community. This thesis presents a simple method for shielding the infrared signature of a jet engine from heat seeking missiles. The research efforts investigated two approaches to shield the thermal signature of the Noel Penny Type 401 turbojet at the Texas A&M University Propulsion Lab Test Cell. First, liquid nitrogen was injected through a manifold at a flow rate equivalent to the flow rate of exhaust gases, producing a small temperature reduction in the exhaust but no infrared shielding. Second, water was injected at a flow rate of 13% of the flow of exhaust gases, producing a greater temperature reduction and some shielding. Water was then injected through a manifold at a flow rate of 118% of the flow rate of exhaust gases, producing a substantial reduction in temperature and complete shielding of the infrared signature. Additionally, numerical simulations were performed using FLUENT to support these experiments. Results are presented in the form of thermocouple data and thermal images from the experiments, and in the form of temperature contours and streamtraces from the simulations

Impact of scene decorrelation on geosynchronous SAR data focusing

We discuss the effects of the clutter on geosynchronous SAR systems exploiting long integration times (from minutes to hours) to counteract for two-way propagation losses and increase azimuth resolution. Only stable targets will be correctly focused whereas unstable targets will spread their energy along azimuth direction. We derive here a generic model for the spreading of the clutter energy based on the power spectral density of the clutter itself. We then assume the Billingsley Intrinsic Clutter Motion model, representing the clutter power spectrum as an exponential decay, and derive the expected GEOSAR signal-to-clutter ratio. We also provide some results from a Ground Based RADAR experiment aimed at assessing the long-term clutter statistics for different scenarios to complement the Internal Clutter Motion model, mainly derived for windblown trees. Finally, we discuss the expected performances of two GEOSAR systems with different acquisition geometries.Peer ReviewedPostprint (published version