Greet Deruyter

A commuter-based two-step floating catchment area method for measuring spatial accessibility of daycare centers

This paper puts forward a commuter-based version of the two-step floating catchment area (2SFCA) method, which has gained acceptance in studies on spatial health care accessibility. Current implementations of the 2SFCA method are static in that they consider centroid-based night-time representations of the population. The proposed enhancement to the 2SFCA approach addresses this limitation by accounting for trip-chaining behavior. The presented method is illustrated in a case study of accessibility of daycare centers in the province East Flanders in Belgium. The results show significant spatial differences in accessibility between the original and commuter-based version of the 2SFCA (CB2SFCA). They highlight the importance of giving heed to more complex travel behavior in cases where the need for detailed accessibility calculations is apparent.

A GIS-based flood risk tool for Jamaica: the first step towards a multi-hazard risk assessment in the Carribean

The Caribbean is known to be one of the most hazard-prone regions in the world. Hurricanes, flooding, storm surges, earthquakes and landslides lead to extensive material, human and economic losses in the region. The growing intensity of these hazards, combined with the consequences of climate change, rapidly increases the concern among decision makers. Although many researchers have succeeded in developing a single-hazard risk assessment that accurately estimates the risk of one type of hazard, the complexity of the relation between the different types of hazards is causing difficulties in the development of a multi-hazard risk analysis. This research aims to develop such a model. In a first step, the consequences of each type of hazard will be assessed individually, starting with riverine flooding. In the next step, the methodology used in this tool will be assessed and modified to fit other types of hazards. Finally, all single-hazard tools will be combined into a generic multi-hazard risk assessment tool for the region. In Jamaica, local governments use a flood risk methodology that is based on building water defence structures to evacuate the water as quickly as possible. This methodology, however, causes bigger damages downstream. Another method, based on minimizing the consequences of the overall flood, is already in use in many countries. In the Flemish region of Belgium, it is implemented in a tool called LATIS and has already proven to decrease losses after a flood event. Therefore, this risk-based methodology is used as the base for developing the Jamaican flood risk tool. The biggest concern during this research is the lack of data in the region. The methodology used, is based on the Flemish flood risk tool and the acquired data is thus very elaborate. During the implementation of the methods for the Caribbean, especially the lack of sufficient rainfall data and adequate damage functions has proven to result in less accurate damage and vulnerability maps.

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.

Concepts, reflections and applications of social equity: approaches to accessibility to primary goods and services in the region of Flanders, Belgium

Mobility presents a variety of opportunities as it allows users to access locations and services, and to meet people beyond their immediate surroundings. While the concept of mobility primarily focuses on the ease of moving, accessibility delineates the actual potential to participate in out-of-home activities. As a result, accessibility is a complex concept with a multitude of foci. This complexity is presented in the first section, which explains the general concept of accessibility, how it is defined and how it is related to the notion of transport-related exclusion. This section also gives an overview of the body of literature on the measures to determine area-based as well as personal accessibility levels and points out the important contrast between the simple, easy-to-interpret methods, adopted by policy makers and the complex methods preferred by experts. The second section clarifies how the dichotomous relationship between the urban and rural environment is reflected in transport policy that emphasizes on (especially car-based) mobility rather than on accessibility. Furthermore, the environmental and economic points of view are highlighted and the common policy strategies focused on sustainability are illustrated. Subsequently, the shortcomings in the way in which the contemporary debates concerning mobility, sustainability and the social implications of transport planning are conducted, are criticized. Finally, the last part of this section is dedicated to an extensive discussion on the ability of transport policies to, on the one hand, generate spatially as well as temporally uneven accessibility effects that give preference to certain population groups above others, and on the other hand, their ability to strive for a more equitable distribution of transport services amongst the population. The third section proposes two methodologies for measuring transport-related social exclusion implemented in a literature-based case study in Flanders. These studies comprise the following topics: measuring transport gaps by relating the social to the transport disadvantage and measuring modal disparities by comparing accessibility by private and public transport. The former investigates in which areas the provision of the public transport system is not tailored to specific public transport needs. The latter examines the disparity in access by private and public transport in order to highlight the car dependency. Both case studies incorporate the temporal variability in provision through the private and public transport network, as the time-of-day strongly influences accessibility levels.

RISK ASSESSMENT: A COMPARISON BETWEEN THE USE OF LASER SCANNERS AND TOTAL STATIONS IN A SITUATION WHERE TIME IS THE CRITICAL FACTOR

For some time past, terrestrial laser scanning has been adopted as one of the data acquisition techniques for e.g. deformation measurements, documentation of historical monuments and civil engineering projects. Using terrestrial laser scanning, millions of 3D points can be obtained with a high accuracy in a time span of minutes or even seconds depending on the type of laser scanner. However, processing the data still remains a time consuming process. As a result, total station measurements are often preferred over laser scanning for high frequency deformation measurements when time for data processing is limited. In the research at hand, the applicability of terrestrial laser scanning in time critical situations was assessed based on the case of a recent monitoring project on a sewage purification plant. Deformations had to be assessed twice a day in order to prevent accidents from happening. The total station measurements were executed and processed by a specialized company (Teccon bvba, Belgium). At the same time, terrestrial laser scanning was used by researchers of University College Ghent and Ghent University to acquire deformation data. The data obtained by laser scanning was processed independently and then georeferenced to the same coordinate system as used for the total station measurements to enable comparison of the resulting deformations. In order to be able to meet the time requirements, a “quick and dirty” method was developed to process the laser scan data. This method implied no cleaning up of the point clouds and only primitive modeling of parts of the structure. Although a complete 3D model of the whole structure could not be generated in the limited time frame between two scans, the objective, namely an accurate assessment of deformations almost in real time, was accomplished. Furthermore, the degree of detail that can be reached through the use of laser scanning surpasses the possibilities of total stations. Moreover, even with a “quick and dirty method”, visualization is much more comprehensive than can be obtained by using a total station.

Evaluating spatial inequality in pre-schools in Ghent, Belgium by accessibility and service area analysis with GIS

All Flemish regional cities struggle with the effects of spatial and social inequality which is manifested amongst others in the scholar system. Pupils of primary schools (in Flanders children from 2.5 to 12 years) living in the proximity of a suitable school are forced to attend schools at a greater distance because the capacity of nearby schools is exceeded. This often leads to scenes in which parents camp outside the school, hoping they will be able to enroll their children in the school of their choice. The goal of the research at hand was to provide a tool for local authorities, not only to be used to visualize and analyze the current school constellation in their territory, but also to support decisions concerning capacity extensions of existing schools, implantation of new schools or suppression of non-essential school locations. This was done by creating an automated and general applicable model in which GIS and network analysis are used to determine the areas serviced by each school. Furthermore the model is used to produce a coverage map based on the ideal scenario for the current demography which is then compared to the actual situation, thus pinpointing and identifying problem areas for which appropriate measures have to be taken. Finally the model can be used to predict and resolve future capacity issues. The model was validated for pre-schools in the city of Ghent, Flemish Region, Belgium and proved to be a valuable tool to support local policy in education.

The use of terrestrial laser scanning for measurements in shallow-water : correction of the 3D coordinates of the point cloud

Although acoustic measurements are a wide-spread technique in the field of bathymetry, most systems require a water depth of at least 2 m. Furthermore, mapping shallow-water depths with acoustic techniques is expensive and complicated. Over the last decades, the use of laser scanning for mapping riverbeds has increased. However, the level of accuracy and the point density which can be obtained by Airborne Laser Scanning (ALS), and Airborne Laser Bathymetry (ALB) in particular, are not as high as those of terrain measurements originating from ALS. Moreover, ALS and ALB are not yet suited for mapping shallow-water beds. Therefore, more recent research focuses on the use of Terrestrial Laser Scanning (TLS) from either a fixed or static position (STLS) or from a mobile platform (MTLS). An obvious advantage of using STLS and MTLS is that both the river beds and the river banks can be modelled by means of the same data acquisition system. This ensures a seamless integration of data sets describing both dry and wet surfaces, and thus of topography and bathymetry. However, although STLS and MTLS have the potential to produce high resolution point clouds of shallow-water riverbeds and - banks, the resulting point clouds have to be corrected for the systematic errors in depth and distance that are caused by the refraction of the laser beam at its transition through the boundary of air and water. In this research a procedure was implemented to adjust the coordinates of every point situated beneath the water surface, based on the refractive index. The refractive index depends on the wavelength of the laser beam and the properties of the media the beam travels through. The refractive index for a laser beam with a wavelength of 532 nm varies by less than 1% for a wide range of temperature and salinity conditions. Nevertheless, during the case studies, it became clear that it is important to use an estimate of the refractive index which approaches the actual value as closely as possible in order to obtain accuracies of less than 1 to 2 cm. Therefore, the refractive index was determined for each specific case by using water samples.