Annelies Vandenbulcke

Deformation monitoring of a bridge with tram rail infrastructure

This paper describes the monitoring of a bridge with tram rail infrastructure using a Robotic total station, a Terrestrial Laser Scanner (TLS) and an Inertial Navigation System (INS). The presented methodology is elaborated using a case study performed in the city of Ghent, Belgium. Several modalities of dense and heavy traffic cross the historical bridge with a high frequency. In particular, when trams cross the bridge, the tram rails locally move in a vertical way which is visual to the naked eye. This raises concerns that the bridge in itself is also moving and may become unstable, making the infrastructure very vulnerable. If this would be the case, an urgent renovation of the bridge needs to be planned. To investigate whether these costly and imminent renovation works will be necessary, a thorough measuring campaign was set up. Together with the surveying team of the city of Ghent, Ghent University used a total station and a terrestrial laser scanner to monitor the bridge as a whole and the tram rails in particular. An additional experiment with an Inertial Navigation System (INS) was also implemented to monitor vibrations of the construction. A measurement strategy was set up to compare the movement of the rails and the top and bottom of the bridge in rest, as well as during crossing of a tram. The workflow of the data capture and the data processing is described in this paper. Combining all measurements, it is confirmed that the bridge is secure and it can be concluded that only the tram rails have become unstable.

Towards cost-efficient prospection and 3D visualization of underwater structures using compact ROVs

The deployment of Remotely Operated Vehicles (ROV) for underwater prospection and 3D visualization has grown significantly in civil applications for a few decades. The demand for a wide range of optical and physical parameters of underwater environments is explained by an increasing complexity of the monitoring requirements of these environments. The prospection of engineering constructions (e.g. quay walls or enclosure doors) and underwater heritage (e.g. wrecks or sunken structures) heavily relies on ROV systems. Furthermore, ROVs offer a very flexible platform to measure the chemical content of the water. The biggest bottleneck of currently available ROVs is the cost of the systems. This constrains the availability of ROVs to a limited number of companies and institutes. Fortunately, as with the recent introduction of cost-efficient Unmanned Aerial Vehicles on the consumer market, a parallel development is expected for ROVs. The ability to participate in this new field of expertise by building Do It Yourself (DIY) kits and by adapting and adding on-demand features to the platform will increase the range of this new technology. In this paper, the construction of a DIY OpenROV kit and its implementation in bathymetric research projects are elaborated. The original platform contains a modified webcam for visual underwater prospection and a Micro ElectroMechanical System (MEMS) based depth sensor, allowing relative positioning. However, the performance of the standard camera is limited and an absolute positioning system is absent. It is expected that 3D visualizations with conventional photogrammetric qualities are limited with the current system. Therefore, modifications to improve the standard platform are foreseen, allowing the development of a cost-efficient underwater platform. Preliminary results and expectations on these challenges are reported in this paper.

Dynamics of Surface Moisture Content on a Macro-tidal Beach

ABSTRACT Montreuil, A-L.; Chen, M.; Brand, E.; Strypsteen, G.; Rauwoens, P.; Vandenbulcke, A.; De Wulf, A.; Dan, S., and Verwaest, T., 2018. Dynamics of surface moisture content on a macro-tidal beach. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 206–210. Coconut Creek (Florida), ISSN 0749-0208. Surface moisture content is a significant factor controlling aeolian sand transport. It is influenced by atmospheric, marine and sub-surface processes. Although several studies reported direct links in surface moisture content with the processes responsible for those variations, there is still a lack of understanding of its dynamic on a macro-tidal beach. This study aims to investigate spatial and temporal dynamics in the surface moisture content of a macro-tidal beach, and to determine the relative importance of factors controlling these. A field experiment was performed on a dissipative and non-barred beach at Mariakerke (Belgium) during an aeolian sand transport event in March 2017. Surface moisture content was measured from the backshore to the tidal zone using a video monitoring system. Simultaneous measurements of grain size, volumetric moisture content, groundwater level, atmospheric conditions, wind parameters, water level and topography were carried out. The hourly generated moisture maps indicate a clear cross-shore gradient of decreasing surface moisture content from the intertidal zone (ranging from 4–18%) to the backshore (none–8%), while it is more complex in the alongshore dimension. The backshore experienced the most rapid reduction of moisture content below 4% with a dryness rate of the surficial zone reaching 29% per hour in the late morning. It progressively continued to dry in the afternoon when sand strips, mobile aeolian bedforms, were well developed. Changes in moisture content over the beach surface reflect the atmospheric (solar radiation and wind) and marine (tidal elevation, wave and groundwater level) conditions and internal beach characteristics such as bedforms produced by aeolian sand transport and topography. Thus the continuous combinations of direct and indirect interactions between all these factors contribute to the spatial and temporal dynamics of surface moisture content. A better knowledge of the dynamics of the surface moisture content is a necessary prerequisite for the development of models and to compute budgets of aeolian sand transport.

USING 3D MODELLING IN THE VALLEY OF TURU ALTY (SIBERIA, RUSSIA) FOR RESEARCH AND CONSERVATIONAL PURPOSES

Since 1999 the Department of Archeology and the Department of Geography of Ghent University undertake field surveys to the Altai Region in Siberia, Russia. This region is a very important archaeological heritage area in the world. Scattered throughout the region are hundreds of frozen tombs, ritual monuments and petroglyphs. Research of these relics helps to understand the life of Eurasian nomads in the 4 century BC. Even more important, due to upcoming touristic activities and climate change, the documentation of the frozen tombs is imperative. A traditional archaeological survey consists out of a basic description, a drawing, one or two pictures and the GNSS location of each monument. With support of the department of Geography several topographical maps are created based on satellite images (IKONOS, Pleiades) and measurement of Ground Control Points (GCP) on site. Furthermore, since 2012 the use of 3D realistic photo modelling is being applied to survey the monuments in higher detail. The method of photo modelling proves to be successful and cost-effective. Besides their high detail, the almost real-life virtual representation of the monuments makes these techniques less abstract than a traditional archaeological survey. During the field campaigns in the summer of 2014 and 2015 this method was implied to record hundreds of monuments in the valley of Turu Alty (Siberia, Russia). Using 3D modelling software the models are created to document the monuments and petroglyphs of the study area for research and conservational purposes.

Preservation of the archaeological heritage of the North Sea using webGIS

The submerged coastal heritage forms an important aspect of our cultural and archaeological patrimony and offers huge possibilities for scientific and (inter-) cultural purposes. Since the knowledge of this heritage is limited, gathering more data is one of the main objectives of the multidisciplinary project SeArch (Archaeological heritage in the North Sea, www.sea-arch.be). Additionally, these data will be used as a basis for a sustainable management by government agencies. To share, integrate and visualize the gathered archaeological and environmental data and information in a user-friendly way, an interactive web-based Geographical Information System/Service is created. By implementing this webGIS, the benefits of standard map reading (such as providing insight) are combined with facilities such as easy accessible spatial analysis and feature querying in an interactive environment, which is accessible worldwide. To create an interactive webGIS-platform, a good structured spatial database is needed. This paper provides more information about the configuration of the spatial database and the application of the software package GeoServer. The development of a fully functional spatial data infrastructure (SDI) using the most novel, reliable and powerful technological components is described. The objective of this SDI is to increase the accessibility and interoperability of spatial data for a wide range of users.

Procedural city model using multi-source parameter estimation

Most current digital 3D city modelling procedures have either a low degree of automation or require specialized skills. Moreover, the construction process is the result of an equilibrium between the desired level of detail on the one hand and modelling performance on the other hand. Although environmental 3D models and 3D city models in particular are essential for a wide range of applications and disciplines, these difficulties are substantial bottle necks for the availability of the models. In this paper, initial steps and ideas behind a novel approach for the construction of 3D city models are presented using an Airborne Laser Scanning (ALS) point cloud and standard digital 2D data. The first step involves point processing and feature detection for an ALS point cloud, resulting in the separation of building and ground points from vegetation and other points in the point cloud. Secondly, the detected building features are described in more detail using the 2D data, allowing the distinction between roof points and façade points. A texture map is assigned to the detected features using image libraries. The 2D data are also used for the improvement of vegetation mapping. The novelty of this approach is the fact that the actual city modelling is performed using recently made available software. The used software allows the interpretation of conceptual rules for the automated modelling of real-world environments. The proposed workflow is illustrated by the construction of a city model of some part of Geraardsbergen (Belgium).

The demand for hydrographic surveyors in the Benelux

In February 2015, the Hydrographic Society Benelux (HSB) sent an extended questionnaire to 77 of the most important hydrographic companies in the Benelux (Belgium, The Netherlands and Luxemburg). The organization of this questioning was in cooperation with the Department of Geography of Ghent University (Belgium). The purpose was to inquire the demand for hydrographic surveyors during the next 5 years in the Benelux. The Benelux is hosting the four biggest dredging companies in the world, so the demand for hydrographic surveyors is usually fairly high and a good parameter for the general demand in the West of Europe. On the one hand, the aim of the questionnaire was to research the demand for the preferred level of hydrographic surveyor, allowing a concise estimation of the demand for IHO category-A and category-B certified hydrographic surveyors. On the other hand, the required balance between hydrographic surveyors with a Bachelor versus Master degree was questioned. As a similar questionnaire and analysis has been performed in 2009, trends over the past 6 years can be discerned and analyzed. The results are important, not only for the private companies, but also for the higher education institutes. In the Benelux, but also outside the Benelux, one can find hydrographic institutes delivering cat. A and cat. B. IHO certified hydrographic surveyors, combined or not with a Bachelor and/or Master diploma. It is generally assumed that there is a shortage of hydrographic surveyors and/or of hydrographical educated employees in the Benelux. Currently, part of the active hydrographic surveyors in the Benelux are engineers, geologists and other non-specifically hydrographic trained people, who received additional bathymetric trining within private companies. But does this hypothesis withstands a scientific analysis? This will be critically analyzed in this paper.